2020-B4-2

Author Topic: One marker light not working, but blinker does **SOLVED**  (Read 75 times)

BadVRod

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One marker light not working, but blinker does **SOLVED**
« on: May 21, 2020, 09:15:28 PM »
I've searched but can't pinpoint my problem. In my 81, the green dash indicator light stays lit on the driver's side when the headlights are turned on. The side and front markers on the driver's front are not lit. All the other side marker lights are working fine. Blinkers work fine even on the driver's side front markers. Hazards work fine. Changed the bulbs, no difference. Checked voltage at the bulb socket and get very low voltage. Ideas?
« Last Edit: May 22, 2020, 05:02:26 PM by BadVRod »
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b_hill_86

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Re: One marker light not working, but blinker does
« Reply #1 on: May 21, 2020, 10:56:35 PM »
Definitely check the grounds. I had a similar problem a year or two ago. I honestly still don’t know 100% what caused it but I believe it was a bad ground in the socket for the park/turn signal. I cleaned the contacts, tried a million types of bulbs, and at one point I think I switched sockets to see if the problem followed one and I think it did but I can’t remember.

Or if you remove the bulb from the working side I think i you’ll recreate the same symptoms. Basically, I think the parking light power will travel down to the marker light and I to the turn signal circuit (Due to the way the market lights are wired. They have no ground and instead use the parking light circuit as the ground for the signal or vice versa. And when park is on AND signal is activated, the signal illuminates and the marker loses its ground.) . Anyway, since there is no bulb in the parking lamp/signal socket the current can’t flow through to bulb to the ground so it travels back up the signal circuit into the cluster , through the indicator light and to the cluster ground.

I hope I didn’t confuse you.
« Last Edit: May 22, 2020, 07:44:03 AM by b_hill_86 »
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Wallington

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Re: One marker light not working, but blinker does
« Reply #2 on: May 22, 2020, 12:02:38 AM »
And to be more confusing, neither side marker has a full time ground.

BadVRod

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Re: One marker light not working, but blinker does
« Reply #3 on: May 22, 2020, 06:13:49 AM »
Yeah it's all a bit confusing. I have checked the core support grounds and they are solid. The cluster printed circuit is literally like new however I've not probed it to check voltage. I checked the working parking light socket for voltage and I get good voltage at both contacts, but on the non-working side I only get voltage on one contact, and only when the meter is grounded to the battery, if that makes any sense. The marker light doesn't get voltage regardless of ground on the meter, but they both blink when the blinkers are on. Ugh.

This is quite literally the only electrical gremlin I've encountered, everything else works surprisingly. I'll mess with it some more this weekend but this gives me a better idea of what to look for.
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firebirdparts

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Re: One marker light not working, but blinker does
« Reply #4 on: May 22, 2020, 07:07:49 AM »
The bulb in the left front park light is not grounding.  If the ground wire is good, then the problem was just the socket itself and the limited way that the bulb actually contacts it. 

The two hot pins in that park light are connected to the two wires in the side marker.  There's no ground in the side marker.  When the headlights are on, the side marker grounds backfeeding through the turn signal bulb filament on that corner, and that has to ground through the base of that bulb and into the socket.  This backfeeding, which is deliberate, is what makes your interior indicator stick on.

You don't really need to probe anything.  That bulb has to be in for any of it to work.
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BadVRod

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Re: One marker light not working, but blinker does
« Reply #5 on: May 22, 2020, 05:02:08 PM »
The bulb in the left front park light is not grounding.  If the ground wire is good, then the problem was just the socket itself and the limited way that the bulb actually contacts it. 

The two hot pins in that park light are connected to the two wires in the side marker.  There's no ground in the side marker.  When the headlights are on, the side marker grounds backfeeding through the turn signal bulb filament on that corner, and that has to ground through the base of that bulb and into the socket.  This backfeeding, which is deliberate, is what makes your interior indicator stick on.

You don't really need to probe anything.  That bulb has to be in for any of it to work.

THANK YOU! That was indeed the problem. How you explained it made sense. The ground wire receptacle on the park light socket was filthy inside. Pulled the ground out of the socket, cleaned the receptacle and ground contact, reassembled and voila! It's all working. I love easy fixes....Thanks again, everyone!
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Re: One marker light not working, but blinker does
« Reply #5 on: May 22, 2020, 05:02:08 PM »
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