Bob_98SR5

Light Harness Upgrade - 94 Toyota Pickup
By Churnd - 11/12/2002


Churnd shows you how he improved the light output on his rig by replacing the stock wiring harness.

Disclaimer: the write-up is intended to be for Toyota owners with the sealed beam headlights or H4 systems. You might check with the maker of the harness to see if this will work or not with the replacement bulb type headlights.

I was never happy with my headlight output since I bought my ’94 pickup. This is mainly because sealed beams don't put out very much light to begin with, and the stock wiring isn't very efficient. So when I read about an aftermarket wiring harness that bypasses the stock lighting system, I knew I had to have it.

I ordered the harness from Auto Bulb Depot part number AM72064 for $50.

**Auto Bulb Depot has since gone out of business. You can get a similar if not better harness from 4crawler Offroad**



The harness is an H4 ground switch system, made for 2 bulbs, or lamps. This works the same way your stock headlight system works. The headlight has three prongs. One controls the high beam, one controls the low beam, and one is grounded. The high or low beam comes on by providing power to that prong, then through ground… which lights the bulb. I might be wrong about this, but from how the harness was constructed, that's what I came up with.

Installation could not be simpler. The hardest part was finding a place to mount the relays.



I decided at the time to change my headlights out for a whiter light. I picked the Sylvania Cool Blue lamps (6054CB), but only because the store did not have the Silverstar model for my truck. If they had, I would have gotten that instead because it's a brighter, whiter light that would probably respond better to the harness.

One thing that you will have to supply for yourself is two fuse holders and two 20 amp fuses, which will be added to the two wires that are connected to the battery.

One thing I noticed that the picture on the website didn't have was the black box that is wired between the relays. I opened the box up and found two diodes and a 100 ohm resistor. Basically, this box just keeps you from making a mistake with wiring the harness so if you do, it won't mess up the stock system.

Here are the steps for installing the harness:
1. Disconnect the negative cable from the battery (safety first).
2. Unplug both stock connectors from the headlights.
3. Crimp the fuse holders to the battery power wires, and connect the wires to the positive post of the battery.
4. Connect one of the stock connectors with the male connector on the harness. I used the stock connector from the passenger side light because it was closest to the battery for the most power.
5. Route the new connectors to the lights. I unbolted my radiator so I could pass the wire underneath it to make for a cleaner install.
6. Find a good place to ground the connectors. I used one of the body panel screws after I made sure the paint wouldn't interfere.
7. Plug in the new connectors.
8. Drop in the 20 amp fuses into the fuse holders, and you're set!



Seems all too easy, doesn't it? That's because it is. If you're wondering if it actually makes a difference, the answer is yes. I measured the voltage across the prongs using the stock harness, which read 12.6 volts. After the harness was wired and fired up, I then saw an increase to 13.3 volts. The difference can definitely be seen also. It's like I'm driving a whole different truck.