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Old 07-03-2018, 06:50 PM   #1
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Headlight Relay Upgarde Question

I am doing the headlight relay upgrade on my truck and have everything figured out. It says to hook the 12 gauge wire with inline fuse or breaker to the positive battery post. My question is, instead of running the wire to the positive battery post could I use the junction block seeing the big red wire comes from the positive post to the junction block. It'll make for a neater job when I run the 12 gauge wire back throught the wire loom that goes across te top of the rad. I'm thinking it should be okay but thought I'd ask the electrical gurus..
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Old 07-03-2018, 08:15 PM   #2
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Re: Headlight Relay Upgarde Question

I'd rather see you tie into the junction with the alternator cab feed and external regulator wire if you haven't converted to internal regulated alternator.
The junction on the fender is provided to allow the battery to charge from the alternator and to provide an engine off power source or emergency ignition in case the alternator fails.

Keep in mind that the alternator is the primary source of electrical power and every thing should be powered by it with the battery used for starting and backup power.

The headlights won't draw much juice so you could power the relays off the fender junction but it wasn't designed as a main junction. That doesn't look like a fusible link on there now but just a plain red wire.
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Old 07-03-2018, 10:11 PM   #3
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Re: Headlight Relay Upgarde Question

" I'd rather see you tie into the junction with the alternator cab feed and external regulator wire if you haven't converted to internal regulated alternator." Thanks for the response and I was hoping you would chime in on this. I have stock alternator and original type regulator. Could you a picture of where the alternator cab feed and external regulator wire are located. So you also are recommending that I do not run the 12 gauge wire from the positive post?
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Old 07-04-2018, 11:19 PM   #4
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Re: Headlight Relay Upgarde Question

Sorry I haven't been on the forum been busy with the fourth stuff, parade barbeque,etc.

No I wouldn't recommend tieing into the battery positive post but you don't have an easy way to get to the main junction. It's wrapped in the harness just below the left headlight. the factory soldered all the wires together because it was simple and cheap.

Here is a picture of mine after I unwrapped it.

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and a little closer.

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This is a diagram of the factory wiring from the positive post.

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It shows how your wires from the battery,alternator, and regulator, join, and the red power that goes into the firewall block to feed the cab.

These red wires are connected together directly so you can see how splicing the headlight relay power wire into any of them would power the relays.

The alternator post or the no. 3 red wire on the external regulator would be easy places to connect if you didn't want to untape the harness.

Most of the diagrams for the headlight relays call for a 12 gauge wire with a 30 amp fuse to the no.30 terminal on the two relays. A downside with only running 1 wire is that if the fuse blows neither of the relays will work and you won't have any lights. If you run two wires, one to each relay with two fuses then if one blows you will still have the dims, or the brights to get you home.

Here are two diagrams for the headlight relay mods they are slightly different.

The second shows the wire gauge and 2 20 amp fuses and both of them show wiring from the battery positive or any 12 volt source.
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Old 07-05-2018, 09:29 PM   #5
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Re: Headlight Relay Upgarde Question

Thank you for the info. I am planning to use a breaker instead of a fuse and will probably connect as per your diagram throught the Voltage Regulator line. Should I run 2 breakers like you suggested for the in-line fuse or would one be sufficient. .
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Old 07-06-2018, 10:17 PM   #6
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Re: Headlight Relay Upgarde Question

I wouldn't use breakers because they will keep resetting and sending current to the lights if there is a short which could cause an overvoltage to the lightbulbs and blow them out. A fast blow fuse will prevent this until you can determine where the fault is. I would rather pay .50 for a fuse than $30 bucks or more for a light.
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Old 07-10-2018, 12:23 AM   #7
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Re: Headlight Relay Upgarde Question

Thanks for your advice with my project VetteVet. I have decided I want to connect my power wire into that factory mess that you pictured. Do you know of a connector where I can attach those factory red wires plus 1? What did you do with that wire cluster on your truck? I hear on the breaker but am going to run with that this time.
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Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601

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Old 07-10-2018, 01:04 PM   #8
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Re: Headlight Relay Upgarde Question

I dis-assembled all the wires to that soldered junction and attached them to a terminal strip, then I used jumpers to power the wires to each load.

Here's a picture
.

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I haven't completed it yet, still have to wire the cooling fan and a few things to clean up the wiring.

I decided that you will be OK with the relay breakers if you shut the headlight switch off as soon as they start breaking.
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Old 07-10-2018, 05:56 PM   #9
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Re: Headlight Relay Upgarde Question

Thanks for the pic.
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Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601

Ethics is knowing the difference between what you have right to do and what is right to do !!.... Potter Stewart


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