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George H.
George H., Technician
Category: Classic Car
Satisfied Customers: 18668
Experience:  Old enough to have worked on them when they were new
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I have a 71 demon and the back blinkers, tail lights, and

Customer Question

I have a 71 demon and the back blinkers, tail lights, and brakes don't work. I used a test light to see if there was power going to the back lights. Everything is working. I turned on the right and left signal lights and my test light is flashing. Then I touched the ground clip of the test light to one of the pegs in the fixture and the needle part on the other peg. I have a full circuit. When I put the bulb in, I don't have flashing or any sort of lights. I don't know what the problem is. Any help would be appreciated.
Submitted: 11 months ago.
Category: Classic Car
Expert:  George H. replied 11 months ago.

Hello I will help,

It sounds like you have enough current to run the testlight but not enough to run a light bulb. Do you have a voltmeter?

Customer: replied 11 months ago.
I do. What is the proper voltage to make the light bulb work? And how do I increase it?
Expert:  George H. replied 11 months ago.

Put one lead of the meter to a good clean part of the body for ground and with the bulb installed and the brake pedal depressed measure at the green wire to see what the available voltage is. It should be close to battery voltage. If it is low you have a poor connection between the battery and the bulb so we would need to narrow it down from there. If you have battery voltage to the bulb you have a poor ground and then you check the battery to the body and the bulb to the body.

I think you will find you have a poor ground.

Let me know if that is clear and what questions you have, it is important to have the bulb in the circuit so it loads it. A straight pin can be used to get inside connections to measure but your light sockets are hard wired so you may have to pierce the insulation. When you get done measuring use some RTV to seal the insulation again.

Thanks