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Discussion Starter #1 (Edited)
Hi:
I'm trying to help fix my neighbor's truck which i use for a tow vehicle for my tbird track car. It's a 2000 Chevrolet C2500 (3/4 ton truck).

Here's what I've found so far:
1) The STOP/HAZ fuse (20AMP) in the dash fuse panel blows pretty quickly when you press on the brakes. After that, the rear turn signals and brake lights stop working.
2) If you replace the fuse, the hazard lights work without any issue and the door chime works.
3) In an effort to trace the issue back, I have removed the following: the wiring panel for the truck bed lights (in case there was a short there - I recently replaced the bulbs with LEDs), both rear tail light panels (I replaced the pass side one a few months ago), and the wiring going to the trailer lights and rear light harnesses. The STOP/HAZ fuse still pops immediately upon application

Here's what I think is going on:
* All that's left on the car is the wiring harness coming from the dash rearwards to through the frame rail.
* I found the wiring diagrams for this car on autozone.com and I believe the issue might be the stoplight switch shorting out mounted to the brake pedal.
* From one of the diagrams, it seems like the STOP/HAZ fuse feeds into three circuits: stoplamp switch, convenience center/chime module, turn hazard switch. Since the last two circuits seem to work without blowing the fuse, I'm thinking its the switch.

My current plan is to just pick one up from AZ, work my way underneath the dash, hopefully remove some of the extra wiring crap my friend put in this truck (like the lowpass filter+bazooka), and pray that replacing the brake pedal switch fixes the problem (at least test it BEFORE installation).

I also plan to fix the shoddy wiring I found at the rear end (like how the trailer light harness was tied into the stock wiring) but I'm not sure that will fix the issue.

Q: What do you think? Any other ideas on what could be the root cause of this issue?

In one of my wiring diagrams, i did see mention of a rear lamps bussing block. However, when I looked for mention of this online, all I could find was a video. I do NOT seem to recall seeing this back there on a C1500 truck so I'm not sure if this also applies to a C2500. Furthermore, if I did disconnect things between the frame rail and the wiring harness at the rear of the truck, I don't see how this could be the culprit in my specific shorting situation.
https://www.1aauto.com/tail-light-combination-junction-block/i/1altl00929

Regards,
-g
 

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As you said the hazard lamps work, the physical lamps are fine, and the wiring, while ugly was probably ok.

Unplug the connector to the switch; then replace the fuse, and see if shorting the connector pins with a paper clip blows the fuse. :)

Those switches used to be known for going bad and coming apart and causing this in the 70's, so it's likely the switch. :grin2:
 

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Had a simliar issue with my 90 F150 was chaffed wire in the steering column, but I would check the brake switch first like your doing.
 

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do you have one of the short tracers? it sends a signal down the line that can be traced with a radio. when the signal stops that's where your short is.

i have a personal problem with my boat trailer blowing fuses for the brake, turn lights. maybe i need to disconnect them before backing into the water.
 

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i have a personal problem with my boat trailer blowing fuses for the brake, turn lights. maybe i need to disconnect them before backing into the water.
That means the wires have bare spots somewhere and are corroded, making it short out.

Get a new high quality set of trailer lights that are led and sealed, and it will probably outlast the boat. :)
 

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I don't have an answer, but you are not alone with that problem. A guy on a local forum (horsepowerjunkies.com) posted about a similar problem. IIRC, it involved the brake lights always being on, and the hazards coming on with the turn signal. One guy suggested a turn signal blinker being bad.

I would Google it, which will likely take you to a GM forum where other people have had that same problem.

Al
 

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grog6 i have just rewired the trailer with new light kit we found in my dad's barn while moving him. the lights are not sealed though and were just connected with electrical tape.
 

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Discussion Starter #9
I fixed the wiring but I can see how something like this would have a been a ton easier but I'm not entirely sure how it works.

Ever use this product yourself? If seems like if the metal ring conducts enough heat to fuse the wires inside with solder, it would also conduct electricity from inside the connection to the outside world via the very same metal ring. How does the metal ring insulate itself from the solder inside?

The heatshrink bits at both ends are self explanatory.

2) Or, you you just crimp the ring to clamp the wires together and then heatshrink the tubes (not a soldered connection).

-g
 

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Ever use this product yourself? If seems like if the metal ring conducts enough heat to fuse the wires inside with solder, it would also conduct electricity from inside the connection to the outside world via the very same metal ring. How does the metal ring insulate itself from the solder inside?

-g
I've used this technology for years; it's the best way to terminate teflon coax, for one. :)

This is even cooler than you said; the ring is Solder, and it's Inside the HS. (that may not show well, but it is.)

You put it on the wire, twist your wires together neatly, slide this into place and either heat it with a heatgun until the solder melts, or even a bic lighter will work in a pinch. (or a strange spot)

I personally use a "Western-Union" type splice, but it's kinda overkill with solder. :)


When the solder melts into the wire, you seal one end, then work your way to the other, to seal it; the colored stuff is a meltable sealer on the inside.
If you seal both ends before the middle shrinks, your results may not be to your liking. :)

Use the minimum amount of heat you need; the HS will burn. :)

This is waterproof and solid after you're done.

All this said, don't use solder where it will get flexed; it will break right where the wire meets the solder.
A large bend radius helps, but it's a matter of time.
Use this on straight, well supported runs. :)
 

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Way overkill just give me some solder and heat shrink, but I don't use wires that are just long enough like the manufactures. At my last job our saying was, "Better to have a foot too much than be an inch too short." and I personally always made sure to leave enough wire for the guy out in the field to easy make a repair.
 

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Discussion Starter #12
Well this is starting to stump me.
The diagram 2 I have shows STOP HAZ as two separate fuses so this crappy Chilton book must be a generalized manual.
Current flows from there to the stop lights switch. When the switch is triggered, the 20A STOP/HAZ fuse pops.

It does NOT pop if the hazard switch is pushed.
The funny thing is that downstream, there are fuses in the diagram for VEH STOP and CHMSL (whatever that is). Neither are in the dash fuse box.

Any ideas; I'm hoping my friend can find the shop manual for the exact model year truck he owns.
-g
 

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Well this is starting to stump me.
The diagram 2 I have shows STOP HAZ as two separate fuses so this crappy Chilton book must be a generalized manual.
Current flows from there to the stop lights switch. When the switch is triggered, the 20A STOP/HAZ fuse pops.

It does NOT pop if the hazard switch is pushed.
The funny thing is that downstream, there are fuses in the diagram for VEH STOP and CHMSL (whatever that is). Neither are in the dash fuse box.

Any ideas; I'm hoping my friend can find the shop manual for the exact model year truck he owns.
-g
It only takes money.

$225 for a brand new set from Helm: GMC C-Series Medium-Duty Trucks 2000

RwP
 

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It looks to me like part of the diagram you have is a later one.

Look at this page:

https://www.2carpros.com/questions/chevrolet-silverado-2005-chevy-silverado-bed-brake-lights

The diagrams along the bottom show a similar setup to the second diagram, but not the first.

These show the bussing block as well.

If the 2000 is a FBW throttle, this may be the right diagram; it shows the switch go into the flasher module only.



At this point, I personally would apply power to that circuit from a current limited power supply, OR put a headlight bulb I use for troubleshooting such things in series with it, and trace the wiring to the back.

You can power that circuit up by Carefully trimming a 0.187" male quick disconnect to fit into the load side of the fuseholder, make sure you get good contact, so nothing melts. Don't use anything thicker than a fuse blade in that hole...
Apply power polarity correctly, in case there are boxen.
Stay within 0.6V of the battery voltage. :)



An easier, better idea is the light bulb/temporary fuse. :grin2:

An old headlight bulb with the low beam dead makes a good troubleshooting tool; solder wires on, with battery clips or plugs on them, or better yet, solder them to a blown fuse's terminals.
I glued a neo magnet to the base to keep it where I want it.

The headlight bulb only lights when there is a dead short; (it takes ~8A to make it bright) and the flashes and partial lighting while you're moving wires around help you locate the area that's buggered.

It will be a temporary fuse; it will light brightly when the fuse would have blown, and will limit the current enough to protect the wiring from melting. :)

It won't even light for a normal ~3A tail light load or smaller.

I'd unplug all the harnesses I could reach, attach the tester, (or just replace the fuse) try the pedal, then plug them in from front to back until the problem recurs.
 
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