Hello all,

Car: 1987 Camaro Z28

Issue: The LH parking and marker/turn indicator lamps are not receiving 12V at bulb locations, but RH side lamps are. Engine side harness has tested good, and verified 12V connection is missing @ C100 inside the car. I've tested continuity of the LT Blue wire through both sides of the connector on the lower RH side of the steering column, and am wondering if perhaps i'm missing a ground, or if I have an open circuit further upstream at the turn/hazard switch? Wiring diagrams show each lamp location, parking and side markers, have independent grounds, but those grounds are not on the harness (engine) side from what I can tell. Next diagnosing steps? TIA!

Additional testing info : Turn signals are not flashing in rear, but illuminate steadily when actuating the turn signal lever, but also flash when using the hazard button. Horns also not working, but relays are clicking. Fuses are all OK.

 

The front side marker lamps are in series with the turn signal bulbs. This means that they get 12V on one side when the parking lights are on, which of course is also whenever the headlights are on. The other side gets ground through the TS bulb filament. Since the TS filament has FAR lower resistance than the side marker bulb, the entire 12V appears across the SM bulb in effect; let's say, for sake of argument, 11V across the SM bulb filament and 1V across the TS filament, when the TS is not on. Might be even more lopsided that that, iunno, never actually measured it, but that's the general principle. Needless to say the TS bulb doesn't even glow darkly, but the SM glows at near full brightness. This also means that they blink OPPOSITE the TSs: when you turn on the TS, the SM goes OUT when the TS comes ON since at that time BOTH sides of the SM bulb will have 12V on them, and vice-versa.

Therefore, if you have non-working front SMs, first thing to troubleshoot is, the TSs. If they're not hooked up then OF COURSE the SMs won't ever work either, can't possibly, because they're essentially not hooked up either.

The rears are different. They come on solid when the tail/parking lights are on. They get their 12V from the same source as the license plate lights and the tail lights. Are those coming on?

No idea what you're asking. The lights aren't connected to the engine harness at all in any manner way shape form or fashion. Their wiring is completely separate from that. Their grounds go straight to the body. The fronts are part of the front body harness, along with headlights and horn. The rears in fact are part of the "Fisher Body" harness, which comes (came) to the assembly plant already installed to the body. The front harness was installed at the assy plant; the rear harness ends at the "Fisher Body" plug near the fusebox, and the assy plant plugged a plug from the dash/column harness into that. Fronts and rears therefore are completely different as far as how they were built.

 

Sorry to confuse. I know the harnesses are separate, and I was indicating the light harness of which runs into the engine bay and to the lights. What I was thinking, when looking at the wiring schematic, was that there were separate ground leads from each bulb connector location.

My RH SM was illuminating, with no bulb in the TS socket.

Yes, the rear lights are coming on.

 

If it is a Camaro...

The Side-Marker Light-Bulbs are in Parallel (Not Series) with the Front Parking-Lamp Circuit, and the Signal Light Circuit (for each corresponding side).

So the Right Side-Marker Bulb can/ could Illuminate without a Front Right Parking-Lamp/ Signal Light Bulb.

 

The SM bulbs are IN SERIES WITH the TS filament.

Note on the schematic, brn wire 9 is the parking light; and lt blu 14 is the TS. The ONLY WAY the SM bulbs get grounded is, through the TS filament on their respective sides. Except of course for the dash indicator, which is another 194 bulb, just like the SM bulb; if the TS bulb is gone, the dash indicator and the SM bulb will each have 6V across them, and will both glow rather dimly, at ¼ intensity.

The SM bulb will not illuminate correctly without the TS bulb in place and operational. BE the electrons and you'll feel it.

 

I am not going to debate this...
And I will always value your Opinions.

I have worked with and Modified those circuits extensively...
The Side Marker Circuits (Left and Right) will operate without the (Black Wires on the Schematic) Ground Circuits for the Front Parking-Lamp Bulbs

They are a Linear Circuit Design that will use the Brown Wires to Terminate the Circuit (when the Parking Lamps are off).
When the Parking Lamps are ON... they will Terminate on the Light Blue or Dark Blue Wires (when the Flasher has turned off power to the Front Parking-Lamp Bulbs).
Creating the Alternating Signal Flashing (front, then side, then front, then side, Etc).

At the very least, this is the way in which the Test-Camaro operated...
When I designed My All-LED System that replaces the OEM Wiring.

None of the Cars I have built retain the Horrible and Out-Dated Exterior Lighting Systems.

 

So now I'm curious; is the SM/TS wiring different on a Firebird from a Camaro?...

 

I recall it being different...
I do not remember exactly how.

Obviously the 1G2F Cars use Rear Side Marker Lights (1G1F Cars do NOT) as well as Front Side Marker Lights.