1966 Impala headlights cutting out - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 6 (permalink) Old 06-10-2019, 03:49 AM Thread Starter
Join Date: Jan 2019
Posts: 11
1966 Impala headlights cutting out

Hi everyone, I have just discovered I have a problem with my headlights. After 30 minutes of driving my headlights started flickering and cut out completely. After stopping for an hour the lights turned back on but started flickering again after a few minutes. I have noticed the wire from the positive terminal of the battery to the junction block is only 15 guage instead of 10 guage, could this be causing my issue or should I be looking elsewhere for the problem. Thanks for any help offered. Ian
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post #2 of 6 (permalink) Old 06-10-2019, 04:06 AM
Join Date: Jan 2006
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Sounds like a embrittlement open. That is where the wire from the factory was too small (too big a number, since a smaller number buys you a bigger wire), and it was cut too short to reach causing the wire to flex which work hardens the metal until it fatigues enough to break.

In your case a small wire has a lot of broken strands leaving momentary contact followed by excess resistance as the few working strands carry too much current. This results in flickering and brown out. Look for wires half pulled out of terminal s or frayed wiring.

Big Dave
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post #3 of 6 (permalink) Old 06-11-2019, 12:49 PM
Join Date: Jul 2016
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Other possible causes to check out would be a bad or loose ground, bad or loose wiring, the headlight switch and its connections. It can also be caused by a short in the system.

But, the flickering could be an intermittent open rather than a short. I would find the wires near the headlights and start wiggling them as you work back to see if it makes the lights go off.
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post #4 of 6 (permalink) Old 06-11-2019, 11:55 PM Thread Starter
Join Date: Jan 2019
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Thanks for your replys, I have ordered a new loom with relays for the lights, hopefully that will fix the problem. A question on the battery earth, there is a heavy cable from the negative terminal to the engine, also an earth strap from the engine to the firewall, should there also be an earth wire from the battery to the body? Thanks Ian
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post #5 of 6 (permalink) Old 06-12-2019, 09:58 AM
Join Date: Jan 2006
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There are four ground straps) bare copper flat cable with a ring terminal on each end. The motor is grounded to the frame with one. From the negative terminal to the fender (for the front wire harness ground), and two from the motor by way of the two top transmission bolts to the fire wall (one to ground the body while the second has a jumper on the back to fire wall ground that goes to ground the dash wiring).


Big Dave
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post #6 of 6 (permalink) Old 06-13-2019, 12:01 PM
Join Date: Feb 2013
Location: Illinois
Posts: 11
All good answers, but I installed brighter halogen lights in my own 66 Impala. I installed a relay kit to take the new load away from the original wiring harness and to prevent the headlight switch from burning out. Keep in mind, headlight switches have a built-in circuit breaker. I also installed LED bulbs in the brake and signal lights with an electronic turn signal switch. Everything is bright now for night driving.

Lastly, I had previously purchased an aftermarket rebuilt 63 amp alternator. I took the armature & field coils out and installed them in my original alternator case, keeping the correct casting numbers.
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