Alternative Wiring
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4wd High
Joined: Jun 2021
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Alternative Wiring
I'm rewiring my 56 F100, and the service manual schematics and other source documents show a 10 gauge wire running from the voltage regulator to the B terminal on the headlight switch and another 10 gauge wire running from the switch B terminal to the starter solenoid. Power is also sampled at the B terminal and routed to the ignition switch. I assume this was done to accommodate the "charge" gauge in the dash. I have the Batt light in my dash ... so, is there any reason to not just run a 10 gauge wire from the voltage regulator to the starter solenoid and sample the voltage from that point (using 14 or 12 gauge wire) to feed the light and ignition switches? I'd appreciate any input on why this wouldn't work. Thanks
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4wd High
Joined: Jun 2021
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The dash has a Batt indicator light ... basically the same functionality as the oil pressure light. From what I understand about how it works is the light gets power from the ignition switch when you turn it on and a ground comes from the A terminal on the generator (same as A on the regulator) . When the generator starts running the ground is lost, and the light goes out. It's not really a good indication of the charging system's health, but I want to keep the truck fairly original looking.
But if you're asking if a have a multimeter, I do
But if you're asking if a have a multimeter, I do
Phantom of the Phorum
Joined: Jan 2011
Posts: 5,472
Likes: 1,696
From: Kentucky
I'm rewiring my 56 F100, and the service manual schematics and other source documents show a 10 gauge wire running from the voltage regulator to the B terminal on the headlight switch and another 10 gauge wire running from the switch B terminal to the starter solenoid. Power is also sampled at the B terminal and routed to the ignition switch. I assume this was done to accommodate the "charge" gauge in the dash. I have the Batt light in my dash ... so, is there any reason to not just run a 10 gauge wire from the voltage regulator to the starter solenoid and sample the voltage from that point (using 14 or 12 gauge wire) to feed the light and ignition switches? I'd appreciate any input on why this wouldn't work. Thanks
Last edited by EffieTrucker; Jan 24, 2026 at 11:08 PM.
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4wd High
Joined: Jun 2021
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Likes: 6
Thanks for the reply. That's the way I saw it. I believe 12 gauge is good for 20 - 25 amps in a 12 volt circuit, and (per the schematic) most of the wires feeding off of the light switch are only18 gauge so those circuits can be pulling too much current.
Fleet Mechanic
Joined: Sep 2010
Posts: 1,834
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From: Mason City, Iowa
If I am understanding correctly you are wondering about eliminating the 10 gauge run from the battery side of the starter solenoid and the headlight switch B terminal and replacing it with 12 gauge wire and at the same time running your voltage regulator output (Battery)wire direct to the starter solenoid?
About the swap to 12 gauge, I would still use #10. The reason why is lower voltage drop with the 10 gauge wiring. And from the B terminal on the headlight switch your are also feeding your IGN switch, any accesories, and a current hungry ignition coil. 12 would work. But 10 would be better and give you somewhat brighter lights and better spark.
About running your voltage regulator BAT terminal directly to the starter soleniod, as long as you dont have an original ammeter in your instrument cluster like they did on the bigger trucks (and it sounds like you dont) it should be good.
About you BATT light wiring. As long as it is still connected to your IGN switch and the A terminal on your voltage regulator it should still work as before.
Hopefully I understood your question correctly!
About the swap to 12 gauge, I would still use #10. The reason why is lower voltage drop with the 10 gauge wiring. And from the B terminal on the headlight switch your are also feeding your IGN switch, any accesories, and a current hungry ignition coil. 12 would work. But 10 would be better and give you somewhat brighter lights and better spark.
About running your voltage regulator BAT terminal directly to the starter soleniod, as long as you dont have an original ammeter in your instrument cluster like they did on the bigger trucks (and it sounds like you dont) it should be good.
About you BATT light wiring. As long as it is still connected to your IGN switch and the A terminal on your voltage regulator it should still work as before.
Hopefully I understood your question correctly!
Last edited by hooler1; Jan 25, 2026 at 10:07 AM.
Thread Starter
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4wd High
Joined: Jun 2021
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Likes: 6
Thanks for your input. The more I think about it, I think I will run 10 gauge from the regulator to the solenoid and also to the light switch. Electrically, the only difference is that I only have to have one 10 gauge wire in the bundle running through the firewall.
Last edited by tonyginfla; Jan 25, 2026 at 11:07 AM.
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