Weird reverse light problem

[Johnny Atomic]

First time poster. I am having an issue with my 1983 Sierra Classic. The reverse lights work normally when the headlights are off, but they stay on anytime the headlights are on? Any idea where to start troubleshooting.

 

[dvdswan]

Welcome to the site. Maybe check the grounds in the back of the truck for the tail lamps.

 

[Shorty81]

Welcome from the Buckeye State.

 

[chengny]

First time poster. I am having an issue with my 1983 Sierra Classic. The reverse lights work normally when the headlights are off, but they stay on anytime the headlights are on? Any idea where to start troubleshooting.

The lead to the parking/marker lights (BRN) is shorted to the lead for B/U lights (LT GRN).

Inspect the rear lighting harness. Make sure that it isn't pinched between the frame and body somewhere. Also, if any section of the harness is routed close to the exhaust system, check for signs of heat damage.

 

[Johnny Atomic]

The lead to the parking/marker lights (BRN) is shorted to the lead for B/U lights (LT GRN).

Inspect the rear lighting harness. Make sure that it isn't pinched between the frame and body somewhere. Also, if any section of the harness is routed close to the exhaust system, check for signs of heat damage.

This makes sense. I couldn’t think of a way this would happen.

 

[Johnny Atomic]

This makes sense. I couldn’t think of a way this would happen.

If it was shorted this way wouldn’t all the running light come on when in reverse too???

 

[chengny]

If it was shorted this way wouldn’t all the running light come on when in reverse too???

Yes, that's correct. I didn't know if you had checked whether that was the case. For that to occur, the conditions have to be right.

With the H/L switch in off (i.e. not in the H/L's or parking lights position). Move the gear shifter to R.

If the BRN 9 and LT GRN 24 circuits are cross connected, the various lamps in the BRN 9 circuit should illuminate - as well as the BU lights.

To test that the cross connection is with the BRN 9 circuit (and has nothing to do with the H/L circuit), put shifter in P or N, observe no BU lights and then pull the H/L switch out to just the parking lights position.

If you get BU lights - along with parking, marker and plate lights. That would kind of confirm that the BRN 9 is the source.

Another test would be to pull the 20A fuse labeled T/L CTSY. That will eliminate power to the H/L switch for the BRN 9 circuit.

 

[Johnny Atomic]

Yes, that's correct. I didn't know if you had checked whether that was the case. For that to occur, the conditions have to be right.

With the H/L switch in off (i.e. not in the H/L's or parking lights position). Move the gear shifter to R.

If the BRN 9 and LT GRN 24 circuits are cross connected, the various lamps in the BRN 9 circuit should illuminate - as well as the BU lights.

To test that the cross connection is with the BRN 9 circuit (and has nothing to do with the H/L circuit), put shifter in P or N, observe no BU lights and then pull the H/L switch out to just the parking lights position.

If you get BU lights - along with parking, marker and plate lights. That would kind of confirm that the BRN 9 is the source.

Another test would be to pull the 20A fuse labeled T/L CTSY. That will eliminate power to the H/L switch for the BRN 9 circuit.

Great. I’ll check that. This help is much appreciated.

 

[Johnny Atomic]

Great. I’ll check that. This help is much appreciated.

The running lights do come on when put in reverse. So now i know the cause, just have to find the short.

 

[chengny]

The running lights do come on when put in reverse. So now i know the cause, just have to find the short.

Inspect the rear lighting harness. Make sure that it isn't pinched between the frame and body somewhere. Also, if any section of the harness is routed close to the exhaust system, check for signs of heat damage.

 

[Johnny Atomic]

I'll check those. I'll also check the trailer wiring my dad installed 20 years ago.

 

[chengny]

I'll also check the trailer wiring my dad installed 20 years ago.

Ah hah! Might be nothing wrong, but I'd look at that first.

 

[Johnny Atomic]

Fixed. Something to do with the trailer lights. Unplugged the trailer adapter harness from the truck, problem went away. I was originally thinking it was a switch in the column or something, this thread saved me a LOT of time. Thank you!!!!!