Headlight Harness Upgrade

Putco relaysHeadlamp harness

It’s an easy to install supplemental headlight harness.

From the factory, the voltage to the headlight bulbs travels from the battery, through connectors, inside the cabin, to the headlamp switch, and then back out to the lamps via undersized wire and more connectors. It’s not uncommon to find only 10.5 volts at the lamps.

The supplemental harness is installed so that it provides battery voltage to the lamps and is just triggered by the factory wiring. The result is about 35% brighter headlamps and headlight switches that don’t melt and burn out.

Here’s a link to a harness on ebay: http://www.ebay.com/itm/CERAMIC-H4-HEADLIGHT-RELAY-WIRING-HARNESS-2-HEADLAMP-LIGHT-BULB-SOCKET-PLUGS-7-/330997592807

Absolutely plug and play:

  • Remove grille and headlamp bulbs. I fed my harnesses from the passenger side starting between the battery and the back of the headlamp housing, over to the driver side.
  • Plug the driver side bulb into the new harness.
  • Attach the new harness’s ground wire under one of the small bolts on the radiator support after scraping the paint off under it.
  • Attach the harness to the existing harness behind the grille working toward the passenger side.
  • Plug the new harness plug into passenger headlamp.
  • Plug original headlamp plug into receptacle on new harness.
  • Attach the ground for the passenger side just like you did the driver side under a radiator support bolt.
  • Attach relays with provided bracket on the passenger side inner fender.
  • Connect power wires to battery.
  • Revised 1-31-2016

25 thoughts on “Headlight Harness Upgrade”

          1. I commented this above as well, but this is the modification I had to make to a four beam generic harness. In hindsight, it would have been just as easy to do to a two beam harness, just would have wasted two fewer H4 plugs. I threw them in a bag and into a drawer for the future, but doubt I’ll ever give them any use.


  1. Cruiser, I did a dumb thing; I clicked on the link and ordered that harness while reading this tip, only to finish by reading your last comment…I also have a Waggie with the four headlamps. Any idea how I might go about rigging this harness to work? I’d actually be happy if I could get it to only work with the low beams rather than both since I use them 99% of the time anyway. Would greatly appreciate your thoughts!

  2. I have the factory bumper fog lights on my 89 XJ. Will I still be able to use those or will I have to wire them in as auxiliary lights?

  3. I think I have either the answer or a solution. One bulb has 3 wires to it; ground, high beam and low beam. The other bulb has only 2 and it likely is simply jumpered (extended) from the 3 wire connector. Wouldn’t the fix be to cut the extension off the original harness and splice it into the new one? No longer plug-n-play but doable by a Jeeper hehehe

    1. I made it work! Here’s a pinout. The yellow and blue from my generic harness may be different than yours, but the H4 plug will have the same pinout regardless. I ended up running a whole new power line from the harness, and am bypassing the original light switch, keeping hi beam control on the column, by intercepting the load from the switch where it comes off into it’s original white and green wires originate.

      Here’s a link to a quick wiring diagram for the head light harness modification!


  4. Hello, I clicked on the eBay link and put in my compatibility info 93 Cherokee xj 2 door sport 4.0 i6 and it says this harness doesn’t work for it. Do I need a different one ?

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