Ning_85_vette

Guys,
I have a 1992 convertible that i recently bought. one issue I found was that it had the wrong bulb in the right rear brake inboard light. I replaced the bulb with a correct one and the Right Blinker ckt started working normally.

Here is the problem i have now -the 3rd brake light will blink in sync with the right rear lights when i use the right blinker. the 3rd brake light does not blink when i use the left blinker and works as expected. this is with the Headlight switch in the off position. the 3rd light and rear brake lights work normally when not using the blinker. I am going to disconnect the brake light switch at the brake pedal this weekend but i was trying to understand how the 3rd brake light and the blinker ckt could possibly be connected. I am using the FSM for 1992 and using sections 8A-12(Light Switch), 8A-110( Exterior Lights non-DRL parts) and 8A-44(ASR). The only place i see that could link the two light ckts is the brake switch.
So I wanted to ask the forum two questions -

Has anyone experienced this problem before and has a solution?(fingers crossed)

Is there some other ckt or system i should be looking at that involves the 3rd brake light that might explain what i am experiencing.

Thanks
Charles

jmeyer58

I would be willing to bet it is a bad ground for the CHMSL. It uses the same ground as the turn signal and is probably getting feedback with the turn signal. Check the ground connection G401, the manual says it is located rear of the cargo compartment. Good Luck

WVZR-1

CHMSL is independent of the rest of the lamps @ the SLS. The CHMSL shares power from the same as supplied to ASR/ABS.

Try the lamps with "NO BULB" in the inboard socket that you had what you thought was the incorrect bulb. What did you remove for a bulb and what did you replace it with?

Checking the ground G401 certainly.

If the previous owner had a CHMSL issue and decided to use the R/R lamps to power it you would have the situation that you mention also.

Lots to check.

Ning_85_vette

Thank for the reply - I will take the bulb I installed into the inboard rear brake light housing out and test the CHMSL as soon as I can. The bulb that I removed is in the pictures that I have attached(hopefully) - I replaced that bulb with a new Napa BP2057.

To update the symptoms - The CHMSL comes on with the headlight switch in the park position(all of the expected parking lights come on as well). And the CHMSL also flashed in sync with the blinkers when the hazard switch is set to on.

I am still going to look at the G401 ground and I am also looking at checking the C209 connector as it has connections for both the CHMSL(position C209 pin P) and the right rear tail/stop turn lamps(position C209 pin G).

I was hoping that this was going to be a common issue like the turn signaling malfunction that are common. but I think you are correct in that either some prior owner tried to tie in the CHMSL to some power source(in this case the right turn indicator ckt) or there is some way the power side is connected that I need to find. Correct me if I am wrong but it is hard for me to see how the CHMSL can be operated by a bad or missing ground - but knowing Chevy there is probably a way

For now I will check G401 and look for a homemade wiring splice to the CHMSL ckt.

WVZR-1

You've got a lot going on. A possibility maybe, the PO had added the EXPORT(RED/AMBER) lamps and had to modify the SLS to accommodate them. They were maybe later removed. Look for the "white" wire at the SLS being cut. That white wire is the stop through the turn signal switch. The CHMSL shouldn't light "ever" with the HL switch. At the SLS confirm there's a white and blue wire feed and if easily accomplished check with a test light.

With the FSM in hand I believe the first thing I'd do is remove all of the lamps in the rear and confirm the wiring to the lamp sockets. That is pretty straight forward as well as the CHMSL. C209 is likely a hard find.

I'd spend as much time as possible at the rear of the car just confirming the GRN (RH), YLW (LH) and BLU (CHMSL). I'd remove all bulbs and confirm they're correct. It seems there's an issue also with the BRN which would be the TAIL LAMP circuit that allows the CHMSL to light when PL are on. Does the same occur when the HL are on or only PL?

Does the DIC respond as expected with "key on" to confirm ASR/ABS?
I don't know what "key on" should display in the DIC for sure.

Look maybe for a cut/splice where the PO might have added a 4 wire for a trailer. Do you have a hitch? Are there signs of maybe there being one?

With the HAZARDS ON the CHMSL should function independently with the brake pedal STILL.

Does the car MAYBE have RED/AMBER lamps added still?

Ning_85_vette

Ok just to close out this thread, after getting sidetracked with another issue, I finally removed the license plate and found that the light blue wire(ckt 20) had a splice into it - I am guessing from the power side of the left turn signal (ckt 19). I simply removed the wire and now all of my lights are working normal.

thanks to all who helped.

Charles

WVZR-1

It's good when things go well. The "rear of the car" certainly sounded like the appropriate place to start.