Splice into random 12V battery wire? Smart or dumb?

[91Pioneer]

I need to tap 12V battery power, I have exposed the main harness behind the driver headlight.

Is it smart or dumb to splice into there to get 12V battery power to power my aftermarket headlight relays? I will of course put a fuse inline. I *could* run a wire back to the starter relay terminal that has battery power but that seems almost pointless when I can tap into it right here.

 

I see no reason why not if the splice is done properly. There are a few red wires, I would splice into the thickest one.

 

 

[Ωhm]

If you can determine which RED wire goes to C100_D, use that. Fusible Link J would have gone to the headlamp SW anyways for power to the headlamps. Thats the wire your relays would bypass at the headlamp SW.

 

 

[91Pioneer]

Whoa, thanks for the idea. Yeah, I guess one of those wires would go to the headlight switch normally! That is smart thinking right there.

 

Do you know if fusible link J goes to the starter relay terminal? I suppose I could disconnect those one at a time to see when the headlight switch stops getting power??

 

I wonder if I could get away without a fuse then for the new headlight relays since it's already protected by the link. Hmm...

[91Pioneer]

Does your diagrams say how many and what gauge of red wires are passing through that harness? I wonder if the headlight wire feed is thicker than the others due to the load of the lights versus things like the radio, gauges, etc. I am not near the truck anymore but now I wonder if there are different sizes of red wires.

[Ωhm]

1 minute ago, 91Pioneer said:

Do you know if fusible link J goes to the starter relay terminal?

 

All fusible links go to the starter relay terminal.

 

 

2 minutes ago, 91Pioneer said:

I suppose I could disconnect those one at a time to see when the headlight switch stops getting power??

 

Yes. Not sure here but some say two fusible links go to one (1) eyelet. Could cause a problem, if true for Link J.

 

4 minutes ago, 91Pioneer said:

I wonder if I could get away without a fuse then for the new headlight relays since it's already protected by the link. Hmm...

 

I would say your factory protected.

 

[Ωhm]

6 minutes ago, 91Pioneer said:

Does your diagrams say how many and what gauge of red wires are passing through that harness?

 

Power Distribution 4L pg8.pdf

[91Pioneer]

Thanks I'll see what I can find out tomorrow. 4 of 7 links are green so that's already narrowed down a bit. I would bet the headlight wire at the relay goes straight to the wiring harness and along the way as opposed to going into another connector nearby.

[91Pioneer]

Well I found one eyelet at the starter terminal that affected the headlights but it had two wires attached. So long story short 3 wires in that bundle had continuity with the eyelet so I would up guessing which one was the D1 wire at the back of the fuse box on the engine side and tracing that wire back and soldered / tapped into it. I then tapped the ignition wire into the yellow wire in that loom there too that runs along the driver fender well.

 

I did not test yet but I think it's good to go, fingers crossed. I need to replace the washer pump as it is leaking, before I put everything back together.

[Ωhm]

Once again, bummer on that fusible link eyelet with more than one wire. DC Current pickup probe ($$$) would be the only way to solve this.

 

 

1 hour ago, 91Pioneer said:

I then tapped the ignition wire into the yellow wire in that loom there too that runs along the driver fender well.

FYI. Your now running Headlight current (Hi/Lo) through the IGN SW (C268_B3 - C267_I1).

[91Pioneer]

55 minutes ago, Ωhm said:

FYI. Your now running Headlight current (Hi/Lo) through the IGN SW (C268_B3 - C267_I1).

When I say ignition wire I mean the "turn on" wire for the DRL relay, it's yellow. I put it to the yellow wire in the big loom, must be the one you mention. Does that seem like an issue? Yes it should go back to the ignition switch but the draw should be minimal.

 

The actual power draw wire for the DRL relay goes to the fog lamp power wire (10-pin harness) because if the headlights are on the DRLs are off so I'm kind of "power splitting" in a sense. The DRLs power the high beams at 50% voltage.

 

And, the aftermarket HI/LO relay power wires are run to that red wire I discussed, that "main" load runs back to the starter relay as we discussed. The "turn on" signal for the high and low beams tap into the 10-pin harness.

 

As far as I can tell the load is coming from the right places....??

[Ωhm]

Sorry I wasn't paying attention. I was thinking of the HEADLIGHT HARNESS UPGRADE and you were using that wire to power up the RELAYs. oops. Never mind.

[91Pioneer]

Thanks, your help has been invaluable in this and other wiring threads. Pic just for fun.

 

 

[Ωhm]

That going to tidy up and look real nice when your finished.