Strange occurance with headights on

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Steven190

Steven190

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I was driving home after a car show, and with it getting darker earlier I pulled the headlight switch.

I quickly noticed that the turn signal indicators on the dash light up, and the fuel and water temp gauges pegged out to the right. I have not noticed this before. The car has been completely restored with new wiring harness. With the car not running turning on the lights this does not happen. It has to do something with the light circuit grounding?

Anyone have any ideas as to what is going on.
 
Knowing what year model car might help.
I've seen this exact same fault before but can't recall where is was found.
A short circuit could be the cause. There are places where interior lighting gets very close to those other circuits. Steering column wiring is one.
So what do I know...
First check is all ground wires, especially chassis ground connections from front lamp fixtures to battery. A 73 model had a additional ground directly from core support to battery neg' terminal. I'm not sure what year they added that 1.
Current will use the path of least resistance. Maybe that path of least resistance isn't present when the ignition switch isn't on.
 
My 69 dart does the same thing, with the headlights on, my left turn indicator lights up. My temp and fuel gauge are aftermarket so they are not affected. I thought I remembered seeing a thread about that being a poor ground for the turn signal at the radiator support. I never bothered to look into it since I don't drive much at night and it doesn't bother me much anyway. But I could see it back feeding thru the cluster and affecting the temp and fuel gauges because they use that voltage limiter (or whatever it is) on the back of the cluster.
 
Steven190 said:
I was driving home after a car show, and with it getting darker earlier I pulled the headlight switch.

I quickly noticed that the turn signal indicators on the dash light up, and the fuel and water temp gauges pegged out to the right. I have not noticed this before. The car has been completely restored with new wiring harness. With the car not running turning on the lights this does not happen. It has to do something with the light circuit grounding?

Anyone have any ideas as to what is going on.
Click to expand...
You have two clues there. The gauges pegging would suggest a poor ground for the voltage limiter for the gauges. When you turn on the lights the instrument cluster illumination is powered up. When that happens if the instrument cluster has a poor ground the current will go through the turn signal indicators and the corresponding circuit to the turn signals to attempt to ground through the turn signal bulbs.

The first thing I would do is to verify a good ground connection to the instrument cluster. A separate ground wire from the cluster housing to the steering column mount is best.
 
I am sorry it is a 69

Thanks for the info I will check the connection to the voltage limiter.
 
Usually such cross-talk between circuits is due to poor grounds. Newer cars have greatly improved by placing ground studs throughout. Of course they had to w/ the gazillions of wires. In early A's, they relied on metal parts touching and sheet-metal screws, so you may need to run a few dedicated ground wires, as mentioned.
 
For the record, Park lamp power applied to fixtures that have 1157 bulbs. 1 or both fixtures not properly grounded, current back feeds through turn signal wiring and lights up 1 or both dash indicators. This fault has appeared in all sorts of vehicles that use 1157 fixtures. This particular fault should not effect gauges or any other circuits.
Now that I know this is a 69 Dart....
You under dash harness is routed through clips above the inst' panel.
Your inst' panel has 2 rows of contact pins near top edge.
This general area is where faults in this model have been found. Either the harness retaining clips have chafed through wires or contact pins are loose/broken crossing circuits.
At the same time... If the car has courtesy lighting at ignition switch or column mounted shift indicator you have more places for crossed circuits to occur. Good hunting.
 
Thanks It will be a process to find where it is coming from
 
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