1st Gen 4Runner H4 Headlight Conversion

H4 LED Headlight Conversion For Toyota 1985 1st Gen 4Runners and 3rd Gen Pickups


One of the most important aspects of wheeling, is being able to see where you are going. Recently, during our attempted Jeep recovery on the Rubicon, we found out that our OE headlights just didn’t cut it. So, in this article, we will go over how to convert your Toyota OE headlight wiring harness into an H4 plug. This will allow you to run any common headlights in today’s market, that you want. This includes any H4 Led Headlight.


H4 LED Headlight 1st Gen 4Runner
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On our way out of the bowl, it was far too easy to lose the trail at night time. There are road reflectors bolted into the granite slabs that help you find your way at night, but you need to have lights to reflect off of them in the first place. We found ourselves multiple times, having to get out of the #RunnerCrawler to find the trail with flashlights. At one point, we found ourselves roughly 50 feet off of the trail, staring at a 15ft drop off.


The 1985 1st Gen 4Runner OE headlights are terrible options. They are a full sealed housing. Which means that you cannot simply swap out the bulbs like most current headlight housings in vehicles. If a bulb goes out, or you want to upgrade the light output, you have to do the entire housing.


Fortunately, the headlight aftermarket is robust and has thousands of options.


Unfortunately, a majority of those options come in the form of an H4 headlight plug connector.


Do NOT let the OE headlight plug fool you! It looks as though it is either an H4 or an H4656! The stock OE headlight plug is neither of those options though!


H4 Plug Wiring – View from rear side of the plug


During the 1st generation of 4Runner and 3rd generation of pickups, the Toyota engineers did something pretty brilliant. A normal H4 plug runs 2 separate load wires, and 1 common ground. Those 2 loads run your high beams, and low beams. And each circuit is completed through the common ground terminal in the H4 plug.


Toyota 1st Gen 4Runner OE Headlight Plug Wiring


The 1st Gen 4Runners and 3rd Gen Pickups run 2 grounds, and 1 common load. The 2 grounds then run back into the cab and switch on and off in the steering column. This is called “switching grounds”.


This is a great engineering practice, because it means that the load doesn’t have to run all the way back into the steering column. This ends up being much safer, because you don’t have an extra 10-15amps running back through the line at all times, which helps make the switch last longer and reduces the possibility of shorts.



The H4 Harness Conversion Kit




So, in order to convert the 1st Gen 4Runners and 3rd Gen Pickups to H4, you will need to make a convoluted wiring harness with relays and hot wires all over the place… or you can buy one pre made on amazon for about $25.00.


2-Headlight H4 Headlamp Light Bulb Wiring Harness Kit ($25.00)Check Today’s Price!



The wiring harness that helps you convert your OE headlight harness over to H4 is quite simple to setup. It comes all pre-packaged, protected with looms, all connected, and set ready to go. There are 2 relays, 2 H4 female plugs, 2 ground connectors, 1 hot line to the battery, and 1 OE harness connector, and even a few zip ties (which are as good as gold for off roaders!).


If you still have your battery on the passenger side of the engine bay, then the H4 harness simply plugs into the passenger OE headlight harness plug. That will then control when the lights come on or off when you rotate the switch on the steering column. This is done by triggering the relays’ power lines.


Once the relays’ power lines are triggered, they send power from the battery hot line, through the relays to the new H4 headlight plugs; one on the passenger side, and one on the driver side. Each H4 plug then has a ground wire that you just ground out in the engine bay somewhere. Then ziptie the wire loom in front of the radiator and you are set to go!




There are a few nice things about this setup. One is that less power travels a shorter distance. This helps keeps switches intact, and helps to reduce the possibility of shorts in your wiring. Another is that it is plug n play with stock OE headlight harnesses. This allows you to then run literally any H4 plug headlight that you want. Any 5×7 headlight will fit the stock housing spaces.


And the last part is how easy it is to install. It took our friends over at Snail Trail 4×4 a total of about 40 minutes to remove the battery, setup the connections, run the wiring, and put the battery back in strapped down. And they did it with simple, everyday tools that everyone should have in their toolboxes.



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