New to the forum. Trying to save myself a little time having to trace down wires. Hope someone can answer a question for me...

Courtesy, instrument and heater fuses all blowing. So far we've found rotten wiring in the back under the bumper. (Brake, license plate light and trailer connector wires) We plan on changing this harness entirely, but my question is: Would these rotten wires cause the courtesy, instrument and heater fuses to blow?

No wires exposed or touching behind the cluster. Still need to ohm out the courtesy wire under the rocker panel but appears to be okay. Door jamb wires appear okay but haven't checked with a meter yet. So many wires to check.

Help?

 

Just for the sake of questioning, are you replacing the blown fuses with correct amp replacements? Not being an a hole here...I just want to make sure the basics are covered.

 

Good question. I have been struggling with the fuse types. AGC, AGW, AGA an AGX...I know the AG is "all glass" and pretty sure that the last letter designates the length of the fuse. I'm sure we've been using the correct amperage fuse but to be honest we've had a hard time finding fuses in all the above categories at the local AP stores. Will need to get the manual and get back to you on this with some additional info. Since we're on the subject, got any wisdom on the different types of fuses?

 

We definitely have been using the correct fuses. Had to go recheck the manual just to confirm...Here is a snapshot of the fuse specs...


Well, the pic is kind of small but FYI -

Fuses which are blowing:

Heater is 30 amp (AGX)
Courtesy is 15 amp (AGA)
Instrument panel is 3 amp (AGA)

EDIT:

Found a wire loose behind the instrument cluster with a little blue bulb on it. I think it may have been grounding out on something back there. Found out today it goes to the ashtray...Will secure that...

When we put the heater fuse in last night I think it fan may have ran for a second before the fuse popped. Since the fan on low speed only draws about 5 amps it may run a few seconds through the capacitor before blowing the fuse. I guess it puts strain on the capacitor and eventually wears out. I may put another fuse in it and see if it runs on low speed before the fuse blows. Was told that on this model of truck the blower motor is a bear to change out. I wonder if there is a way I can tell if the blower motor is bad without removing it?

Going to check all wires we can which can be connected to the courtesy fuse....Cigar lighter and glove box. Will recheck the dome light and door jamb wires more thoroughly too.

This is my son's truck and we are trying to learn as we go and do it ourselves if possible, so will hold out as long as we can before I give up and take it to my mechanic.

 

Hmm. Sounds to me like there's too much current being pulled through the circuit. Have you checked the amount of amps being pulled on each circuit with your multimeter?

 

Haven't gotten that far yet. To be honest I'm learning all this as I go. I have very little experience at wiring other than basic car stereo stuff and other small things. I've learned more in the last 36 ours than I ever knew before

We will get back on it tomorrow. I pulled the washer reservoir out of my Avalanche tonight since it hasn't worked in years. That pretty much took up all my daylight hours after work today.

 

No problem at all. Be sure to post up your results. If in event you're wondering how to check amperage of said circuits do this:

- remove fuse
- take multimeter probes and place one on each end of the fuse holder
- turn on the truck (or do whatever you do to make the fuses blow)
- report results

This way the meter should read how much draw is on the circuit.

 

You need to isolate and explain the conditions under which the fuses blow (unless it appears to be random).

What specifically do you mean by "these" rotten wires? Do you mean to reference a picture? Your question is poised as though you're looking at something in front of you and talking about it, but we're not there to see what you mean. Which wires, and what specifically is meant by "rotten"? That's a term used to describe wood or food; I'm not sure how it applies to wiring.

 

No specific conditions other than the fuses blow as soon as we put them in. So I suppose random is the best way to describe it...

Maybe "rotten" was the wrong term. I suppose I should have said "brittle and corroded". Also, I thought I was clear on where the wires are located Let me rephrase my question: Would corrosion or electrical shorts of any kind connected to brake/tail light/ license plate light wires which are located under the rear bumper contribute to blowing any of the fuses I mentioned?

I suppose the tail lights are connected somehow to the instrument panel or dash lights since the headlight switch dims the dash lights.

 

Thanks for the tips Dave, that was good information... We will be sure and run those tests soon, hopefully tomorrow. However it may be next year before we get to it

I'll be sure and check back in with any results.

 

Thanks for the clarification. To answer your question, the rear lighting is completely isolated from the courtesy lamp circuit. Rear lighting loads are protected by other means (either separate fuses, or a breaker in the headlight switch).

If the fuse blows as soon as you put it in, something downstream is shorted directly to ground. The courtesy lamp circuit is at a heightened risk for this since most loads are unswitched and hot at all times (making it difficult to troubleshoot). You'll need to look for a short along any GREEN with YELLOW stripe wiring, which runs to a 3-terminal junction behind the glove box (which then runs to the cigarette lighter), the headlight switch (for the dome light), as well as both door jamb switches (again for the dome light).

 

Sounds like good information. I thought it had to be some sort of grounding problem causing the blown fuses but didn't really know where to start. Lots of wires and I'm no genius when it comes to that sort of stuff. I appreciate your advice and it seems like really easy directions to follow.

Thanks again greatly for your help and we will be sure report back with results as soon as we can. Maybe more questions too

 

Listen to fmc400...get a miltie meter or a simple ground and probe test light. Take on one elec problem at a time, since the circuit are separate.

Looks for a smashed flat wire in the bundle up under the cab where the main harness comes under the cab by the e brake cable area or back by the fuel tank.

Did the PO wire in a trailer light connector or electric brakes, that can cause problems.

The spring loaded door switches can cause you some fits along with a faulty headlight switch. FYI it rotates to increase/decrease the dash lights brightness and get the dome light to come on with the doors closed.

License plate light is bad for corrosion and the brake light spring loaded switch is up under the dash by the brake pedal arm.

One problem at a time, and no worries cause fmc400 talked me thru my wiring issues one color coded wire at a time.

Welcome to FTE.

 

X2 ^^^ that guy's good with electrical gremlins

 

Good is an understatement..... but there alot of folks on here with all sorts of skills and experience.