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#1
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1968 GTO Rear Passenger Turn Signal
Need help with Rear Passenger Turn Signal on 1968 GTO
Problem: Head Lights On Brakes On Turn Signal Clicked On for Passenger Side Outer Bulb on Passenger Side Blinks Inner Bulb on Passenger Side does NOT blink - it stays solid No Issue when repeated for driver's side Troubleshooting Done So Far Head Lights Off Brakes Off Turn Signal Clicked On for Passenger Side Outer and Inner Bulbs on Passenger Side Blink in tandem No Issue when repeated for driver's side Next Item Tried Used connection wiring from Passenger Side and plugged into Driver Side Head Lights On Brakes On Turn Signal Clicked on for Passenger Side Outer Bulb on Passenger Side Blinks Inner Bulb on Passenger Side does NOT blink - it stays solid Was unable to switch driver side connection to passenger side. Next Item Tried Disconnected the grounding strap on inner passenger bulb Sanded area and connected a wire for grounding to the socket Went back to passenger harness connected to passenger housing Head Lights On Brakes On Turn Signal Clicked on for Passenger Side Outer Bulb on Passenger Side Blinks Inner Bulb on Passenger Side does not blink - it stays solid No issue when repeated for driver's side. Next Item Tried... Same as the last one except we removed the ground wire on the inner bulb And now the passenger side bulbs blink but not in tandem. The inner goes on while the outer is off. Then vice versa. This is our last gremlin for inspection... Any thoughts? Michael
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Michael 1968 GTO in a bunch of pieces right now! |
#2
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1968 GTOs used a fiberglass molded bucket assy for the rear bumper mounted tail lamps. The sockets inside were grounded to the rear bumper which in-turn was ground to the frame of the car via the bumper mount brackets.
After many years the ground straps for the tail-lamp buckets are often rusted, broken, loose, damaged or missing. Some buckets used flat steel "straps" for the grounds and others I have seen use a flexable mesh weave very much like braided copper ground strap(s). There are 3 lamp sockets per each Left and right so the straps sometimes are not grounded well to the separate sockets. Either way I would check those first.
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Peter Serio Owner, Precision Pontiac |
#3
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Thank you for the response Peter.
We actually removed the housing, sanded the area, and then used a wire for grounding. Same problem.
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Michael 1968 GTO in a bunch of pieces right now! |
#4
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Have you checked the front turn signal housing ground? Those fronts have 2 "+" wires and perhaps a ground in the plug in. I know the bulb sockets do sometimes come "un-grounded" from the steel housing as the housing gets old and water leaks inside.
Have you checked the wiring in the front where the headlamps plug-in? There should be a single black wire; one per each side, that runs off of the headlamp plug(s) and then it grounds to the core support via a ring terminal?
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Peter Serio Owner, Precision Pontiac |
#5
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I performed some bench tests trying to replicate your problem.
Two possibilities: 1. The 1157 bulb is installed backwards somehow. The brake/turn signal filament is on the parking lamp circuit and the parking lamp filament is on the brake/turn signal circuit. The brake/turn signal filament is so bright that it dominates and appear solid when the headlamp switch is turned on. When the headlamp switch is OFF, you see the parking lamp filament pulsing, albeit dimmer but visible and in sync with the other bulb. 2. There may be a series resistance of 2.5 ohms in the affected socket's pigtail to the brake turn/signal filament. This will dim the pulsing to the brightness level of the parking lamp filament; however, you would see some flickering. This flickering is subtle and may look solid if ambient lighting is bright. Hopefully it's one of these. The outer and Inner bulbs are tied in parallel and It's very limited how one can get one to behave differently from the other. I attached a wiring diagram and a chart form of your tests if it can help anyone else solve your problem. |
#6
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Yep ... I'd swap bulbs from inner to outer to see if the problem follows the bulb.
The original sockets get pretty hinkey after five decades, sometimes you can stuff a bulb in there the wrong way and it will "fit".
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I'm World's Best Hyperbolist !! |
#7
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On those old real lamp sockets, probably back as far as the early 1970s GM did acknowledge that there was a problem during the car's original lifetime with 1968 and 1969 taillamp sockets and they did offer a service pack to field-repair the copper "touch" ends. The ones where there were those springs underneath.
I think I have part of one of those "kits" left here; if any interest I would post a photo. The springs can rust or get weak over time and that ends up; you think the bulb(s) are in there but one of the ends has intermittent or no contact with the car's trunk wiring harness.
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Peter Serio Owner, Precision Pontiac |
#8
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Ok... we have a winner.
We removed the light bulb turned it 180 degrees and reinstalled it. Both now flash in tandem. Thank you for the great troubleshooting. Next step... inspection lanes! And at some point body work! Thank you! Michael
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Michael 1968 GTO in a bunch of pieces right now! |
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#9
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As mentioned by Pete
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Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express |
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#10
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Cool bit of trivia there OG. You seem to have all that stuff
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I'm World's Best Hyperbolist !! |
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