eBronc's Electrical Page
eBronc's Electrical Page
I previously had this under the "Tech" section, but it's
grown so large and I've gotten so many emails for more info, I decided it
deserved it's own page. All wire colors are what are in MY harness..the factory
diagrams (and your truck) may vary. Wire colors expressed as "Color/color" show
the first Color as the main wire color, the second as the stripe color.
The constant hot panel will receive power directly from the hot side of the
starter solenoid, and will feed all the electrical loads I want available even
if the ignition is off-headlights, running lights, hazard flashers, stop lights,
horn, radio, and lighter plug. This way, I'll be able to flat-tow the Bronco and
use it's own battery to power the taillights, controlled by a wiring harness
I'll make that'll tap into the Bronco's harness. I'll also wire the starter
switch to constant hot so I can bump the engine over without starting it, and
use the starter to move the entire truck (in granny low) if needed.
The switched hot panel will be fed through the 40-amp relay, and will power
the accessories I'll only be using with the engine running-the heater fan, the
wipers, the ignition coil (duh), and the gauges.
Each circuit will now have it's own dedicated fuse or cicuit breaker, so a
short in one component won't disable something else, and it'll make
troubleshooting much easier-plus I won't have to mess with those fragile glass
tube fuses anymore, and replacements can be found anywhere. The fuse panels will
be mounted up under the center of the dash, as high as possible to keep them dry
during those deep water crossings and garden hose interior cleanings I expect.
Speaking of the dash, I've modified (surprise) it quite a bit by moving the
speedometer/gauge package to the center, doing away with the radio cut-out and
moving most of the controls and switches around-the wiper and hazard switches
are now to the left of the steering column, the ignition key switch has been
replaced with a waterproof, military-spec safety-covered toggle and waterproof
momentary starter pushbutton (found at Aircraft Spruce & Speciality -great selections and
prices!), and the radio will be up in the overhead center console formed by the
roll cage (once it's installed). I installed a covered 20-amp power outlet
(lighter plug) in the large hole that the igniton switch used to reside in, to
power air compressors, spotlights, etc.
The brake lights, turn signals, and hazard flashers all use the same bulb
filaments in the turn signal housings-but it took me a little while to figure
out how they managed this without having them all come on (even the fronts)
whenever the brakes were applied. Here's how they did it:
This way, the front and rear blinkers are only connected inside the turn
signal switch, and in such a way that the brake switch only sends power to the
rear bulbs-the fronts and whichever rear blinker is on only receives power
through the turn signal flasher, which is constantly making and breaking the
circuit as long as it's on. The hazards flash all 4 bulbs at the same time, but
the front and rear outputs are only connected when the switch is on-this
prevents power from the brake switch from flowing to the front whenever the
brakes are applied.
Remember, the front and rear blinker/running lamps are dual-filament
bulbs-one filament is brighter than the other. The brakes, blinkers, and hazards
all use the brighter of the two-the parking lamps use the dimmer one.
The running/parking light circuit is easy-power comes in from the fuse box on
the Black/orange wire, then from the headlight switch out 2 brown wires-1 to the
LF bulb low filament and then on to the RF bulb low filiament. The other goes
out to the LR bulb low filament, then on through the license plate light and on
to the RR bulb low filament. The front and rear side marker lamps are wired in
paralell with the running lamps.
The headlights are simple, also-power comes in from the fuse box on the
Black/orange wire, through the headlight switch, then out the Red/yellow to the
floor-mounted dimmer switch, where it EITHER goes out the Red/black wire to both
low beams, or the Green/black wire to both high beams. Simple-except all the
current has to go through the headlight switch, dimmer switch, and all that
wiring before it gets to the headlights. That will be changed in my truck. I'll
be using relays to handle all the current for both low & high beams, and
just use the stock headlight and dimmer switches to activate the relays. This
way, I'll be able to safely and easily run 100+watt bulbs without overheating
the stock wiring. Here's a great explanation of the concept and procedure.
Ignition switch:
Headlight switch:
Turn signal switch:
Wiper switch:
To power my re-wired electrical system and accessories, I needed an alternator. I had tried rebuilding the stock one with a kit from Quick Start, but even after numerous tries and retesting, I never could get it to produce any current, so I gave up on it.
Checking the Ford-related bulletin boards and web sites made it clear that the "3G" was the way to go when upgrading, so I did a little more in-depth research and realized that 130 amp 3G alternators came stock in various Ford, Lincoln, & Mercury cars and trucks in the mid-to-late 90's, so there were numerous mounting configurations. An interesting fact I discovered on eBay is that if it's listed as a "3G", it's pretty damn expensive..but if I searched for, say, a "Taurus alternator", I could find the exact same 130 amp alternator for around $20 or so (used, of course.)
I actually ended up buying TWO 130 amp 3G alternators - one from a police-package 3.8L V6 Taurus that didn't work, but had the right type of mounting ears on the case ($10), and the other one was a new take-off unit off an E-350 cab & chassis that was being converted into an ambulance ($25), but had the wrong type of mounting bolt pattern for my 351W. I simply took them both apart, cleaned everything, then took the best parts from each and reassembled them into just what I needed. It turned out the Taurus alternator just had a broken brush wire, so I fixed that and now have spare parts if I need them.
Testing the alternator at the local AutoZone showed a healthy 14.5v output. Cool.
When I got the truck, the electrical harness had
already been ripped out-and after taking a good look at it, I found out why. The
Black/yellow main charging wire that feeds from the alternator up through the
ampmeter in the dash was melted-must have been a pretty major short to ground.
The front and rear turn signal wires were cut at the hazard flasher switch plug
and twisted together-I guess to bypass the switch, since it wasn't there. Other
than that, all the other wires were intact and had continuity, and the switches
that were still there worked OK after just a little cleaning and a shot or two
of WD-40. Figuring out where everything went and what it did took a little
detective work though, since I hadn't ever seen it in the truck, hooked up to
anything. I found a few Bronco wiring diagrams on the web, downloaded them, and
compared them to the harness I had-of course, mine didn't match any of the
diagrams I could find-but it was close. It took many hours to figure the
circuits out by staring at a slightly out-of-focus black & white print with
tiny little numbers describing wire colors, probing wires with my multimeter,
and making lots of notes...but I finally did. I learned quite a few interesting
things along the way, and came across some methods the factory used to complete
circuits that just struck me as STRANGE. For example:
The original fuse box was badly corroded, and since I was
planning to modify the harness anyway, I decided to replace it with 2 new ATO
(plastic blade-type) fuse panels-one constant hot, one switched by the ignition
and fed by an isolating relay (so the ignition switch won't have to handle all
the current itself.) JC Whitney had the best deal I could find on what I was
looking for-$12.00 each for the bare panels and $6.00 for the 40-amp relay.
Brake lights: When the
brakes are applied, power comes from the headlight switch(!) on the Red wire,
through the stoplight switch, out the Red/black wire to the turn signal switch
in the steering column, then out the Green wire to the bright filament in the
RR bulb AND the Yellow/black wire to the bright filament in the LR bulb.
Blinkers 
When the turn signal lever is
moved to the left turn position, power comes from the 14Amp fuse through the
Orange/yellow wire to the turn signal flasher, out the Blue wire to the turn
signal switch, then out BOTH the Green/white wire to the LF bulb bright
filament(and the indicator in the speedometer face) and the Yellow/black wire
to the LR bulb bright filament. When it's moved to the right, the circuit up
to the turn switch is the same, but the outputs are the White/blue wire to the
RF bulb bright filament(and the indicator in the speedometer face) and the
Green wire to the RR bulb bright filament.
Hazards: When the hazard light
switch is activated, power comes from the 20A fuse through the Red/white wire
through the hazard flasher, out the White/red wire to the hazard switch, where
it splits and goes out on 3 different wires: Red/black to the turn signal
switch, then out to both rear blinker/brake bulbs: White/blue to the RF
blinker bulb, and: Green/white to the LF blinker bulb.
None of this means anything any more for my truck, since I won't
be using a keyed ignition switch-but I put it here in case it might help
someone track down a problem in thier own truck.
Since I changed the wiring system so much (plus the fact that I just don't find them very useful) I decided to get rid of the original ammeter in the gauge cluster and put a voltmeter there, instead. I bought a cheap generic 2" round voltmeter off eBay, then took both it and the stock Bronco ammeter apart to combine the two into something that would fit the gauge opening and give me what I wanted. I ended up using the stock ammeter face after painting it black to hide the amp markings, then applied dry-transfer numerical decals from an R/C car decal cheet to show volt levels. The needle I shortened a little and painted bright orange. The ammeter face fit over the voltmeter guts with just a little work, and some epoxy glued the two together. I "calibrated" the hybrid gauge by hooking both it and my digital test meter up to a spare 12v battery, then crimping the needle over the shaft so it agreed with the digital meter. Adding either resistors inline to lower the voltage or a D-cell battery or two to raise it showed a corresponding change at the meter face, so I'm confident it's as accurate as it needs to be.
Golden Rules and the Basics
With most cars, the body and frame serve as one of the "wires" that feed each
circuit. Usually, the car body and frame serve as the negative side of each
circuit (the ground), and the positive side of the circuit is fed with a wire.
If a device is not properly attached to the body or frame, or the attachment
point is corroded, the circuit is compromised and will not function properly.
The first thing to do when a circuit fails is to make sure it is grounded
properly.
Individual wires do not (usually) fail. Insulation may crack or burn off, but the wire
will still conduct electricity. The only time a wire will fail is if it is
physically damaged, cut, broken,- ( or melted.) Damage can usually be detected by following along the wiring loom
and looking for cuts. If the outside of the loom isn't damaged, it is (usually) safe to assume the wires inside aren't
damaged, either. If you suspect a bad wire, read on-wires don't just go bad, but
connections do.
Connections at the ends of wires fail regularly. Sometimes, they break or
come loose. Other times, they corrode. Factory wiring harnesses usually do not
hide connections under tape or other wrappings. (Really? My
Bronco's harness had 5 or 6 of them.) When tracing a problem,
follow the harness and verify that each connection is clean and functional.
Switches, sensors, light bulbs, and microprocessors are all electrical
components that are susceptible to failure. Components with moving parts, that
generate or receive heat, or that are exposed to water or other corrosives are
the most likely to fail.
In almost all cases, it is better to repair a factory circuit than to rewire
around it. Adding circuits for new accessories is one thing, but don't change
the way one left the factory. Most factory electrical systems, including
much-maligned Lucas systems, were carefully designed by trained engineers and
work perfectly well until corrosion or component failure sets in. Shadetree
mechanics who wire around factory circuits usually do so out of a lack of
understanding. They often take shortcuts or make mistakes which can be dangerous
(read as "will burn up a car").
Tools Needed
Another helpful tool is a voltmeter. Voltmeters come in two flavors, digital
and analog. Each type has advantages and disadvantages, but either works well
for diagnostics. Pick the type you prefer in the cost range you can afford.
Voltmeters are usually combined with other measurement features. One typical
combination is the Volt/Ohm meter, which includes the ability to measure
resistance of a circuit in ohms. The other typical combination is the engine
diagnostic meter, which usually will measure dwell (for points ignitions),
current (amps), and include a tachometer function. Volt/Ohm meters are available
from under $20 to much more. Engine diagnostic meters are more expensive-plan on
spending at least $50, and much more for a high-quality unit. If you have to buy
just one meter, start with a cheap Volt/Ohm meter. Get a few pieces of jumper
wire with insulated alligator clips on the ends. It's a good idea to include an
inline fuse in the jumper wire in case of mistakes or problems. A few wire
brushes and a battery post cleaner should round out your electrical tools.(I'm partial to my Fluke 77 digital multimeter, myself.)
Troubleshooting Basics
After these preliminary checks, use the test light to test circuits as
follows:
If these steps do not help solve the problem, keep in mind that it could be
multiple problems. For example, a device may suffer from a bad ground and a
loose connection along the positive side of the circuit. Two or more
simultaneous problems are much harder to troubleshoot than a single problem. If
you are still stuck, keep reading about common problems and solutions, or
consider turning the problem over to an expert.
Common Problems. Common Solutions. Common Sense.
Dead Battery
Slow Battery Drain
Alternator Over- or Undercharging
Crank Starter, Everything Goes Dead
Sticking Heater, Accelerator, Clutch, or Choke Cables
Dim Headlight
Brake Lights Turn off Taillights
Turn Signal Problems
Blown Fuse
Intermittent Problems
Wiring Additional Circuits
There are several golden rules for solving
problems with automotive electrical systems. Corrosion is the biggest reason for
failure. Wires do not (usually) fail. (Well, they do if they melt.) Grounds, connections, and individual components fail regularly. And
in most cases, it is far better to repair a faulty factory circuit than to
rewire it. Corrosion is electricity's biggest enemy. Battery terminals, fuse
blocks, sensors, switches, connectors, and grounds are likely to fail because
they are corroded. Cleaning or replacing these connectors will repair a great
percentage of electrical problems.
Given these common problems, a 12-volt test light is an
essential tool to diagnose and trace an electrical failure directly to its
cause. A quality test light looks like an awl with a light bulb in the handle
and a wire sticking out of the top. It should have a sharp point and an
alligator clip at the end of an 18- to 36-inch-long wire. These lights are
available for under $10, so every toolbox should have one.
Before troubleshooting a circuit, check and clean
the battery terminals and check all fuses. Make sure the battery is fully
charged. If a fuse is burned out, don't just replace it and think the problem is
solved. Fuses blow for a reason. Find out WHY.) The circuit affected must be further tested to determine why the
fuse burned out. More on that later.
1. Check that the test light is working. Attach the alligator lead to a
ground, and then touch the pointed end to the positive side of a circuit. The
positive battery terminal or a terminal on the fusebox are good test
points.
2. Test the positive lead at the device. Leaving the alligator lead
attached to the same ground that was used to test the light, touch the pointed
end of the light to the positive connection of the device that is not working.
If the light glows, there is either a bad ground or bad device. If the light
does not glow, trace the positive circuit that leads to the device using Step
4.
3. Test the ground at the device. Connect the alligator clip from the test
light to the positive lead of the device, then touch the pointed end of the test
light to a bare metal portion of the device, to its ground strap, or to a bolt
that attaches the device to the body or frame. Ensure that you touch the pointed
end of the light to bare metal, as paint or other coatings will not conduct
electricity. If the light glows, you have power to both sides of the circuit and
most likely the device has failed. If the light does not glow, clean or replace
the bolts, nuts or ground strap to the device. A wire brush and/or sandpaper can
be very effective for this.
4. Test the positive circuit that leads to the
device. Ground the test light's alligator clip. Test the light again to ensure
the quality of the ground. Working backward from the device, follow the positive
wire to its switch, sensor, or source of positive current. Test the circuit at
each connection along the way (i.e., each terminal block or snap connector). If
the light glows at each connection after the switch, suspect the switch. If the
light stops glowing at a connection, clean or replace the connector.
5. Test a switch, if applicable. To test a switch, check that there is positive power to
the switch by touching the positive lead on the "input" side of the switch. If
the light does not glow, continue to trace the circuit back to the fusebox or
battery. If the light glows, touch the positive lead on the "output" side of the
switch. (A manual may be helpful here to show the location of these leads.) Move
the switch through its range and see if the light ever glows. If the light does
not glow, or glows in the wrong switch position, replace the switch.
Occasionally, a switch can be repaired by spraying it with WD-40 or a similar
lubricant/corrosion fighter. However, this is usually only a temporary
fix.
6. Test a sensor, if applicable. To test a sensor, microprocessor, or
other black box, refer to a manual for testing instructions for that specific
item. This is one area where more sophisticated equipment is often needed.
Alternatively, replace the sensor or item with a known working item. The latter
method is not usually practical, as new electrical parts are generally not
returnable and few people keep working spares.
This set of problems and
solutions is common to most cars, and dealing with them doesn't require a lot of
specific electrical knowledge, just some common sense. Of course, these are very
general and may not work for some specific makes and models. If these don't
work, consult a manual or an expert.
Charge the battery for at least one hour. Check for clean
connections at the battery terminals, starter and grounds. Use the starter to
crank the engine over five or six times. Attach a voltmeter to the battery and
watch its reading as someone cranks the engine several times. The voltage should
stay at 12 volts when the engine is not cranking. If the voltage drops below
eight or nine volts while cranking, or the engine won't crank any more, suspect
the battery. If you suspect the battery, and it's not very old, charge it longer
and test it again.
If the battery is draining overnight or over the course
of a few days, some device is still turned on and draining it. To find the
cause, disconnect the negative battery connection. Use your test light to jump
the negative battery cable to the negative post on the battery. If the light
glows, something is turned on. Disconnect fuses and/or circuits one by one until
the light goes out. Trace the circuit that was causing the light to glow to find
which device is still on. Dome lights, trunk lights, alternators, and
non-factory accessory circuits are common causes of such drains. Radio memories
and dash clocks usually are not drains and will not make the light glow for this
test.(My parents' conversion van had a visor courtesy lamp
that stayed on all the time and kept draining the battery..they didn't find it
for 8 months.)
Attach a voltmeter to a good ground and
a good positive lead. (Usually, the battery works best for this.) With the
engine switched off, the battery voltage should read 12 volts. With the engine
running, the voltage should read 13.5 to 14.5 volts. Below 13.5 volts usually
signals a non-working charging circuit. Check for a tight belt, and clean
connections at the alternator and the battery. Also make sure the engine is
properly grounded. Above 14.5 volts usually signals a bad voltage regulator.
Either way, the solution is usually a new or rebuilt alternator.
Sometimes everything will seem just fine until you crank the starter, then nothing
will work, not even the dome light. Starting with the battery terminals, remove them and give them a good
cleaning. Then clean the ground strap to the body and to the engine. Then clean
the positive connection to the starter. One or more of these connections is
corroded. The load of the starter causes arcing at the corroded connection,
which weakens the connection. Since these connections are the main power
connection for the whole car, they shut everything else down when they get too
weak.
What does this have to do with electrical problems? Plenty. If the engine ground
strap goes bad, the
engine will seek another ground through these cables. Often, the car will run
and start just fine. Over time, however, these cables will melt themselves to
their housings. Replace the affected cables and clean or replace the engine
ground strap.
Sometimes, one or both headlights will be dim. One of the
headlights has a bad ground and is grounding itself through the other headlight.
In doing so, the headlights change the wiring configuration from parallel to
series. When wired in series, they each share half the voltage and glow dimly.
Clean or replace the ground(s).
This is a variation on the dim headlight
problem. A bad ground is causing the brake lights to ground themselves through
the taillight circuit and vice-versa. Clean up the grounds, and everything will
work fine.
When a bulb burns out, most turn signals will either
flash quickly or not at all. Sometimes, they do so even though all bulbs appear
to be working. Other times, they may flash, but very slowly. If both left and
right circuits act the same, suspect the flasher unit or the switch. If only one
side has a problem, corrosion is at work. The solution is to first check and
clean all the grounds, which often requires removing lamp assemblies to clean
the bolts and attachment points with a wire brush. Sometimes, the base of a bulb
will corrode, and simply replacing the bulb will solve the problem. Other times,
the bulb socket is corroded and should be cleaned.
Finding the cause of a blown fuse can be difficult. A component
in the circuit is either dead-shorted to ground, or is causing too much load on
the circuit. If something is dead-shorted, fuses will blow the instant they are
replaced and the circuit is turned on. Physically search the wiring in the
circuit, then disconnect components attached to the circuit one by one until you
find the short. If something is generating too much load, the diagnosis is
similar, but more difficult. Try to isolate any device on the circuit and see if
its use blows the fuse. If you still don't find the problem, check a manual or
consult an expert for testing each device and ensure each device is in spec.
Intermittent problems are the hardest to solve. If
you can't get the problem to happen while you're looking for it, shake the car
or the wiring harness and see if that causes it. Loose or corroded connections
are common causes for intermittent problems and such shaking will often bring
them about. If you still can't solve it, call in an expert.
First and foremost, follow the accessory
manufacturer's instructions. However, many instructions suggest wiring directly
to the battery to ensure a good power supply. Avoid this if possible. First see
if there is an available accessory circuit in the factory wiring that can handle
the necessary current. Many factory systems have extra accessory circuits and
fuses built in for owners to expand. If you still want to wire directly to the
battery, make sure you have a fusible link, fuse, or circuit breaker as close to
the battery as possible. Also, avoid the self-resetting circuit breakers since
they may reset before you know there is a problem.
