H4 Wiring Harness Questions

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Jul 7, 2014
Hi all

Man I love this forum. I was asking a question in the 95 and older truck section and had another question about a headlight mod, sure enough there is a lighting section!

I have a 1987 4runner. Let me just say the factory light output is terrible. I have done a great deal of reading on this upgrade and am planning to make my own replay harness. Attached is a picture of the schematic I drew up (I tried to scan it but the scanner wasn't working, will post scanned version later). Daniel stern's lighting website was very helpful, as I basically just copied his diagram. However, after learning about negatively switched headlights on Toyotas, I tweaked his diagram.

My question for the electronic pros out there, does this look correct?
My second question is what gauge wire should I run out of the relays to the headlights? I'm planning to run 12 gauge from the battery and 14 gauge for the ground wires. However after looking at H4 connectors, most use 18 gauge wire. That just seems too small in my opinion. I think I would rather run 14 gauge all around except for the 12 gauge power supply wires to the relays.

Consider running 12 gage for your headlight ground wires too. The heavier gage will benefit both sides of the light.

As for the diagram it looks correct to me from what I remember.

Also you don't need heavy gage wire from the switch to the relay.
i got the IPF headlight harness from front range off road a few years ago for my 88. totally plug and play. went with hella e spec headlights. what a difference in performance. crisp with a very sharp cutoff for traffic. they are not DOT compliant, if your state is a stickler for that.
Thanks everyone for the info! I have to check out Blue Sea's Circuit Wizard.
Also, I saw the front range harness but thought I read somewhere that the high beam indicator light didn't work after it was installed.

Users who are viewing this thread

Top Bottom