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Rear Brake Lights Problem 2003 Chevy Silverado

Sfc Bittner

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Sfc Bittner Enthusiast

Sfc Bittner

Posted
Posted

Here is the Problem.

 

When you step on the brakes the dashboard shows the left turn signal (solid light) the front turn signal comes on solid at the same time.

The rear brake light on the left (both) come on. The right side rear brake light (top) comes on but the lower one that serves as the turn signal/brake light does not light up.

The center brake light works.

 

Troubleshooting that I have done.

 

Tested Bulbs both have the same bulb and if I remove the bulb from the left light and place in the right light I get the same results. Both bulbs are the duel filament bulbs.

 

1. Test turn signals all work.

2. Test reverse lights all work

3. Test 4 way flashers all work

4. Test 12VDC from the junction block (Rear Brake light circuit board) On C1 pin B (BLUE Plug) I get 12 vdc from pin to ground

4. Test 12VDC on C4 (Black Plug) Pin A I get 12 VDC from pin to ground

5. Test 12 VDC on C4 (Black Plug) Pin G I get 12 VDC from pin to ground

6. Test 12 VDC on C4 (Black Plug) Pin C I get 12 VDC from pin to ground

7. I tested continuity for the circuit following the light blue wire all the way to the Stop Lamp switch at the brake pedal all checks good.

 

What would be my next course of action? Any Help is greatly appreciated.

ChevyTech77 Senior Enthusiast

ChevyTech77

Posted
Posted

You have a poor ground.

 

Disconnect trailer connector and look for green. Repair as needed.

Reground the tailights at G401. (main rear frame ground on top of frame by spare tire hoist)

Sfc Bittner Enthusiast

Sfc Bittner

Posted
  • Author
Posted

ChevyTech77

 

Ok I found the ground wire you were talking about I removed it and then tested the brakes the 2 lights that did not work now work when the brake is applied however none of the others do.

 

So I know it is a ground problem just need to isolate where.

 

So an update.

 

With Ground wire G401 Unattached The lower right side brake/turn signal light works and the right lowest parking light works.

 

Where should I check next?

 

Thanks.

ChevyTech77 Senior Enthusiast

ChevyTech77

Posted
Posted

What happens if you disconnect the right rear tail light assembly and leave everything else connected like it should be?

Sfc Bittner Enthusiast

Sfc Bittner

Posted
  • Author
Posted
What happens if you disconnect the right rear tail light assembly and leave everything else connected like it should be?

 

 

Doing what U asked If I disconnect the right rear

 

When pressing the brake pedal the left rear lights all work both the top and bottom along with the lowest one the parking light all light up. The left turn signal light stays solid.

Sfc Bittner Enthusiast

Sfc Bittner

Posted
  • Author
Posted
What happens if you disconnect the right rear tail light assembly and leave everything else connected like it should be?

 

 

Doing what U asked If I disconnect the right rear

 

When pressing the brake pedal the left rear lights all work both the top and bottom along with the lowest one the parking light all light up. The left turn signal light stays solid.

 

I am still looking for advice if anyone could help thanks.

ujtruck Enthusiast

ujtruck

Posted
Posted

Could be wrong type bulbs in rear ?

 

*** wrong bulb can create short circuit inside that holder

 

flip your head lamp selector to park lamp, and apply brake then post your results

 

if you can separate the front lamp plug from the rear then post your results

 

check connector around foot forward of the rear bumper - i think its on drivers side

 

parking lamp circuit (left) receiving power via brake circuit or missing / poor ground connection, check G100

 

is your Turn Signal / Multifunction switch good ?

 

its hard to troubleshoot problem like this over TCP/IP protocol :)

Sfc Bittner Enthusiast

Sfc Bittner

Posted
  • Author
Posted
Could be wrong type bulbs in rear ?

 

*** wrong bulb can create short circuit inside that holder

 

flip your head lamp selector to park lamp, and apply brake then post your results

 

if you can separate the front lamp plug from the rear then post your results

 

check connector around foot forward of the rear bumper - i think its on drivers side

 

parking lamp circuit (left) receiving power via brake circuit or missing / poor ground connection, check G100

 

is your Turn Signal / Multifunction switch good ?

 

its hard to troubleshoot problem like this over TCP/IP protocol :)

 

 

Thanks for your reply.

 

Bulbs I know are good. They have been checked and rechecked.

I know it is very hard to troubleshoot this way I am willing to call someone if they think they could assist me. Just send me a message.

 

I think my problem is I do not have the full schematic.

 

When I get home tonight I will check this and post results. (flip your head lamp selector to park lamp, and apply brake then post your results)

 

Where is (check G100) Located?

 

is your Turn Signal / Multifunction switch good ? From what I have seen yes But if you could let me know exactly as to how you are checking the switch I will reconfirm this.

 

Thanks for your help. Any and all help is greatly appreciated.

 

Now for an Update. This is what I have done over the weekend.

 

I noticed that when I took off G401 That the Right Rear Brake/Turn Signal Light would work and the Left Rear Parking Light would work. With the ground wire G401 Unattached.

 

I then took out the whole Right side wiring harness checked for continuity all wires check good. I did the same for the Left side wiring harness all checked good. I traced the 2 wires that come off G401 the wires right above the spare tire 1 small I believe black wire and 1 thick black wire. They go across the rear bar and back to the rear of the truck main thick black wire goes down to the trailer ground then back up into the rear circuit board connectors.

 

I hope this is not sounding confusing and I am getting my point across.

 

I then cut the black middle wire off the right rear brake light/Turn Signal to try and isolate. Both light worked but they were very dim. So I know it is a ground fault somewhere just do not know where.

 

V/r

John B.

 

Ps. If you would like to assist me via phone I can call you or you could call me. I am on East Coat time and normally home after 6 pm. Thanks again.

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  • 3 months later...
benallen13 New Member

benallen13

Posted
Posted

Does anyone know where I can find a diagram or list of what does what from the rear junction box. I have also seen some ground wires refered to as #'s, is there a list or diagram where I can find that? I am in the process of installing a flat bed on my truck and do not have any diagrams for the truck or the bed. Just a test light and some guess work. I tried briefly tonight to get everything hooked up but was unable to find the light designated for my brake lights on the flat bed. This may sound like a crazy question but .. Whats the difference in wiring into the wires from the junction box and just splicing into the loop of wires running across the back of the truck. As you can tell, im no mechanic but am willing to try anything once..

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