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Old 04-15-2017, 03:23 AM   #1
Northwest Outlaw
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Lost Headlights

1961 Apache 10, SBC 350 swap, single wire alternator, headlights were working both high and low. I installed a Sunpro Tach and Voltmeter and lost headlights when I started the truck.

After the install I turned key to "on" and voltmeter read 12v. Then I turned on the lights to see what draw they have on the voltage. The gauge bounced a little and dropped to 11/11.5 and I turned them off. I started the truck to test the tach, it works. After I shut off the engine I went to turn on the headlights and running lights and got nothing. The parking light harness wires were warm.

The tach and voltmeter are plugged into ignition leads on the fuse block and grounded to sheet metal under the dash. The voltmeter is in the cluster but wires straight to the fuse block and ground. I did remove some unused wires from the cluster harness: the water temp, oil pressure light, generator light. I took the wires and blades out of the terminal plugs.
All the work was done with the negative battery post disconnected.

I'm new to all this, first car project. Looking for help walking through all the trouble shooting that will find the issue.
Thanks
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Old 04-16-2017, 03:00 AM   #2
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Re: Lost Headlights

And I found the culprit...
New switch ordered
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Old 04-16-2017, 02:45 PM   #3
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Re: Lost Headlights

Looks like it might be time for the headlight relay mod. Very easy to do for 2, or 4 headlights GM or chevy.


Here's a diagram of each.

Name:  HeadlightRelayWiringDiagram mod.jpg
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Name:  GMC%20Headlite%20Relay%20Diagram%201.jpg
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Old 04-16-2017, 11:37 PM   #4
Northwest Outlaw
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Re: Lost Headlights

This looks interesting. I'm not very familiar with wiring, is the mod to add the relays for high and low beams? Is there a full write up on doing the work?
Thanks again
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1961 Chevy Apache "BoomStick"
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http://67-72chevytrucks.com/vboard/s...d.php?t=694506
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Old 04-16-2017, 11:58 PM   #5
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Re: Lost Headlights

I found this answer you gave on another thread. I think I understand what's going on, please correct me if I'm wrong. There is a relay switch between the lights and the switch, one each for the high and low circuits and the relay needs power feed and to be grounded.
My questions are probably basic, but like I said I'm new to all this.
A) What does the relay do? I'm assuming it's something similar to a fuse to keep the wires from getting hot?
B) What type and where would I get the relays needed?
C) does placement of the relay matter? I know the high and low wires both run through the dimmer switch inside the cab, or between the firewall plug and the radiator support. Would either of these locations work and is one better than the other?
D) Power source for the relay, should it come straight from the battery or come from the fuse block? I'm assuming it should be always powered, not keyed powered, since the headlights can be turned on without the key

I'll do more research as well.

Thanks again for all the help.
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1961 Chevy Apache "BoomStick"
-First build, lots of plans, little experience. What's the worst that could happen?
http://67-72chevytrucks.com/vboard/s...d.php?t=694506
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Old 04-17-2017, 03:18 PM   #6
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Re: Lost Headlights

I found all the threads about the headlight relay mod and think all my questions are answered. Ordered relays, in line fuses, dimmer and headlight switch.
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1961 Chevy Apache "BoomStick"
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http://67-72chevytrucks.com/vboard/s...d.php?t=694506
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Old 04-23-2017, 04:31 PM   #7
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Re: Lost Headlights

Along with new headlight and dimmer switches, which made my lights work again, I did the relay upgrade. Ran separate, fused power leads from the horn relay junction to each the high and low beam relays. I was able to connect the tan and green wires and plug from my harness to the relay plugs and make a pretty clean and understandable install. Got a little worried when the high beams weren't working at first but was able to trace it down to one of the blades in the harness plug not sliding into the connector on the firewall.
Thanks again for the help
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