Custom Headlight Harness Build

Started assembling. So far here's what I'm learning:

1. the relay/fuse holder I'm using feels cheap and the terminals don't fit perfectly snug, but it seems like it will work.

2. 20 gauge wire for the trigger wires is super small and annoying to work with.

3. I'll be mounting the relay box further back in the engine bay than I thought. I bought enough wire, but it's good to keep in mind the distance from the battery.

4. Relays with the tab on them will have to be trimmed to fit in this box. No big deal, but would be nice to have plain square ones in the future.

 

Assembled the harness today, going to have to redo it. More things I've learned:

1. A blow torch is not a good heat gun for shrink tubing. Guess I should buy a heat gun.

2. Heat tubing with adhesive inside is a bear to pull several wires through. Don't bother.

3. Making your own connectors is not worth it, buy ones with pigtails.

4. Measure twice.

5. 05-11 tacomas have H10 fogs, not H11

The harness works, it's just a bit lumpy and there's a problem with one of the connections. I'm still well within budget, and I can reuse most of the materials to redo it. Now that I've had practice crimping and organizing all of the wires, I think it will go smoother in round 2.

 

1. blow torch? Yikes. A bic lighter works. A BBQ lighter works. A microtorch works if you move it around fast. Yeah the heat gun is the proper tool for the job, but I don’t always use it. You have to be very careful not to set it on something that will melt. Carpet, seat, floor mat.

2. Heat shrink with adhesive is awesome. That’s all I use. It shrinks 3 to 1, whereas the regular stuff only shrinks 2 to 1. Sounds like you’re using too small of heatshrink. Although some of the Harbor Freight stuff is cheeseball, their plastic box of heatshrink is actually pretty good.

3. There are special crimpers just for fusebox terminals. They curl the 2 tabs around and into the middle.

4. OOPS!

5. OOPS!

 

Okay guys, I need help. Yesterday I assembled the harness and tested it. I had it wired for dual (87/87) relays, but only had standard relays on hand (87/87a). When I went to test it, I did not connect the passenger side, which would be the side connected to the NO (87a) terminal.

To reiterate, I only tested the driver side of the harness. For some reason the driver bulb was very dim with the low beam, but the bright worked fine. After putting all of the wiring back to stock, all lights worked fine.

I drove for about an hour last night and my headlights worked fine. This morning I started my truck and only the passenger side headlight came on. Then, about a minute after starting, my passenger low beam burnt out. Both high beams still work.

Is this just a crazy coincidence? Everything is currently wired as stock, and I never touched either bulb.

TL;DR tested my harness, driver low beam dim, returned to stock, both low beams stopped working.

 

How old were the lamps?

 

Probably at the end of their life. I run them all the time and put on quite a few miles. Just seemed like too much of a coincidence happening the day after I mucked with the wiring.

 

I guess all you can do now is check the voltage on both sides & compare. If it’s the same then I’d say you’re pretty much good to go.

 

I checked the voltage when I was testing the harness, and I was getting a full 12.1V with the engine off. Seemed like enough, but yeah comparing is probably smart.

To clarify my understanding, would a voltage drop at one of the headlight terminals be an indicator of faulty wiring or a poor connection somewhere?

 

That’s a bugaboo only you can determine. Start by lookin’ for green connections, corrosion & such to start with.

 

Alright, sorry for the delay. I finished the harness last week and it turned out great! I ended up using ribbed wire loom for the long runs of wire, and it is much cleaner and easier to work with than heat shrink wrap. The relay/fuse box looks really clean.

The only issue I'm running into is the light output. I have a Hella 100w/80w in the driver side and an Osram 100w/90w in the passenger side for comparison reasons. The lights are actually surprisingly comparable as far as my eyes can tell. This being said, the low beams don't seem nearly as bright as what other members have experienced with this upgrade. The foglights and high beams have great output, but the low beams don't seem much different than before the upgrade. I measured voltage drop, and I'm at 0.7% driver/1.3% passenger, which means that is not the issue. My truck currently has a negative rake until I upgrade the rear leaf springs.

I'm going to see how the lights look after I get my rake back and clean the lenses. If I'm still having output issues with proper rake, clean lenses and minimal voltage drop, I'll have to do more investigation.

 

Here's my quick light output pics, not great because the truck is on an incline.

 

Eager to see how this ends up for you. I’m ready to do it to my 2002 taco. I was hoping you would see a big difference. I’m going to get new headlight housings too since mine have almost 700,000 miles on them