Tow Truck Fuses Keep Failing

My daughters car had a similar problem and I found a wire that had been rubbing metal and had worn through the insulation and shorted out. Pulled the wire away from the metal and added some tape so she could get to my heated garage for a permanent fix.

Not sure if this is it JE, but I had a similar problem that turned out to be an overcharging alternator.

It culminated in quite a light-show when it burned out the head lights (and every other bulb in the truck) and melted the fuse box.

JE, now the odd electrical problem can be a pain to trace down, but what you indicated is happening would suggest that you have 3 seperate circuits all grounding out. Or is it one fuse that keeps blowing and its cutting out the 3 circuits you've stated.

Whichever the problem is happening after the fuses and the one common place where all these circuits go is in the steering column to the stalk switch, maybe something has rubbed through a harness there or been pinched somehow and is grounding out causing the fuses to blow.

Cold weather is tough on batteries and starter motors, but generally the colder a cable is, the less the resistance is in that circuit (only measureable in milli Ohms), so that shouldn't cause any grief.

Give me a clue as to how many times the fuse/s have been replaced and if it is one or 3.

Paul BB

Ask if your friend washes the ice melting compound off daily it is detrimental to electrical connections.

BWIRE makes a good point. Check for leaks in the windshield/firewall.

By all means, carefully inspect the wiring at any point where it may be subject to wear. Look also at connectors for stray wires that didn't make it into a crimp.

Salt water is very conductive. Check for missing mud flaps or other missing protective covers in and around the wheel wells. Salt drenched melting snow splashed up into the area under the hood may be part of the problem.

Bob's #1 rule of auto repair states that "The last one that touched it screwed it up." The circuits that you mentioned are all used on the emergency warning light bars on the tow truck. I am of course guessing that the dash lights are off because the tail lights are out. There is some place that the tow truck body receives electrical power from the truck chassis. Usually this point will be at the foot-well area of the driver's position, or the back of the truck chassis, where a trailer towing harness would hook up to. If the light bar is on the cab, I would start in the cab. If the light-bar is on the tow truck body or the subframe of the hoist assembly, try to follow the wires as they lead down from the light-bar itself. Suspicious places are where the wires pass through a section of steel, or are strapped to a section of the body. Good luck.

The most common is corroded trailer light connector

I'm assuming the dash light failure was actually a tail light fuse

Pinched or chaffed wiring to the rear could also do that

On wreckers, commonly the factory rear harness is adapted to the wrecker bed, and the trailer connector at the rear of the left frame rail. This additional wiring is usually the problem.

Being so cold the wire insulation is brittle. steering column harness would be vulnerable along with the hook up in the back as bob c pointed out

I agree with Guest regarding corroded connectors. Fords were notorious for this in the 80's commonly resulting in massive amounts of smoke just prior to the fusible link burning up.

I didn't see any references to some brake work being done on the truck by anyone, but here is something that we experienced with one of our trucks.

We had to have our rear brakes rebuilt at a local Ford shop. They always do excellent work, but shortly after the unit returned to the department, one of the water rescue personnel advised me the brake lights, turns, dash lights and license plate lights suddenly went out, this was on a left turn, first one initiated after a trip of about 33 miles.

After checking my fuse boxes, I got beneath the truck and done some deep inspection along the left frame. We had this unit undercoated, and what I found could escape inspection unless you were really looking. This included some tugging while watching the slack in the wire loom move.

There is a nut with a large wing that is designed to allow only so much turning when the mechanic is refastening the brake cable, which also has the wire loom attached nearby by a factory plastic clip.

What had occurred was when the cable was reattached after the repair, this wing on the nut had indeed turned to bind against one of the horizontal sections of the frame. In the process of tightening the bolt that holds the cable and wire loom, the wing sliced into the wire loom as it became entrapped between the end of the wing and the bottom horizontal frame, and thus my "short". I could not see this upon my first inspections, and had to literally worm my way up into the frame area because the undercoating hid the problem area perfectly in black.

Maybe there is a clip or wing somewhere like this instance that has been stressed, intentional or not, that has intruded into the wire loom.

I even exposed the wire loom in the kick trough under the door's plastic cover to inspect that section as it takes on sand and salt water often. Hey, out of sight, out of mind.

Good luck. I'll check on this thread over the next few days.

there has been some good suggestions already but I would add that when hunting for a short I hook up a digital DVM between ground cable and neg. battery terminal. Have everything shut off , set meter for maximum amps (usually 20 amps for short periods), have one guy watch meter while other guy wiggles wiring looms and open wiring. Also if the short is in a lamp you can usually find it because it will be hot to the touch.

Thanks for all of the great comments..

They have been helpful.

Today my buddy came by with his tow truck.. it has a twenty foot bed and there was plenty of ice and snow along most of the wiring in the back and along the rails.

It took a good hour with a heater, hammers torch and other stuff just to get most of the ice off.

Not everything is fixed, but some lights are indeed working again. (fuses replaced too)

One front left turn indicator was broken and shorting against the frame, but that was an unusual broken harness situation that had probably developed over a period of time from the looks of it... the weather just helped things out..

....SO.. now..

The lights that were not working but are working again include... back-up lights.. brake lights.. dash lights.. left turn signal on the left rear and light bar... (and presumably in the now disconnected and previously shorted indicator on the front of the truck.

Currently the problem that remains is that while the front right turn signal does operate, the indicator on the rear bumper and in the light bar will not flash for a right turn, or in hazard operation... (although they DO light up as running lights)

I did a basic inspection of harnesses and the light bar connection.. it all seemed pretty modern and decent on this Chevy .. still, there is a lot of loom covering a lot of wire. and i yanked a lot looking for snags.. none noticed..

...another look is in order.. but we ran out of time today.

Unlike the front turn indicator, the light bar and rear turn indicators are likely part of the brake light system which are controlled through the steering column loom. If this is the case you will find a 2 element lamp at those locations; one for tail and one for stop/turn.

Check the lamps first for one burned element, then work back through the brake light connectors.

GA. If my memory on GM wiring is correct, the green wire from the turn signal switch goes directly to the right rear turn signal lamp filament. The brake function of the truck uses this same wire when you step on the brake pedal. When you turn the directional lever to the right, or left, the connection from the brake switch is disconnected, and the green wire is now connected to the turn flasher. If the filaments are not burned out, it is time to check the wire on the turn switch.

Possible the light bar/rear indicator use an independent flasher module.

hi JE,

one trick i have used is to get as much working as possible, then at night turn on everything with the engine not running. turn off the lights. then with a small flashlight start wiggling every harness and wire on the vehicle, one at a time. real easy to see the sparks that way.

or

my mechanic uses an electrical short finder. they make cheap ones for under $30. he has a better one that has a two foot long wand with a sensor on the tip. allows him to run the probe along harnesses and componenents. tells him when he is near a short.

good luck. stay warm.

joe

With a little practice you can use a portable "CB" for short detector too

That is what you should have asked. What you did ask...hard to figure, if ya get my drift! Said another way: all non-defective fuses fail until they succeed.

By "flat bed tow truck" I'm going to assume you mean something like a stake bed truck with tow hitch (5th-wheel, ball, and/or pintel) for attaching a towed vehicle. You did not mention a towed vehicle pulled when the overload occurs, so...can assume it's not the towed vehicle lighting harness. It is uncertain what you meant by fuses (plural), so it must be assumed you meant repetitive blowing of a single original fuse and its replacements. If this interpretation is correct, then the logical first place to look is in the trailer lighting hookup wiring (and connector) of the towing vehicle...as this is exposed to weather, flexion, chafing, etc,...and far more likely to be at fault than interior chassis wiring. If the wiring fault is found to be caused by flexing or chafing, good idea to protect the exposed wires with spiral wrap after repairs. Next consider replacing the flasher (using heavy duty flasher); in fact, periodic (every few years) flasher replacement is a good practice especially when frequently connecting towed vehicle lighting and in severe weather; or at least keep a spare handy.

Note to web host/master: the words, flexion and pintel, are missing from the spell-check vocabulary, so a being erroneously flagged.