I noticed my headlights were dim. Started troubleshooting, found 11.6 volts at the lights. Got schematics from a chiltons manual, traced voltage to and from the switch. basically I am losing 1.5 volts through the switch. 13 volts in 11.6 out. Going to replace the switch. Has anyone ever seen this before?

 

The switch won't cause that big of a voltage drop to cause dim headlights.

What's it read on the headlight socket?

I would order:
H4 housings
80/100w H4 bulbs
And get 30' of 10 gauge wire and 2 40 amp relays and make your own harness of headlights unlimited times better than the stock ones.

 

11.6 at the headlight.

there is a red wire with a white stripe that feeds the switch. then If I remember correct a brown/yellow that goes from the switch to the headlight. I have a fluke 189 with the real sharp pointy leads. poked the leads through the wire to check voltage.

 

What's it check coming into the switch? The switch won't cause a 1.5 v volatile drop.

 

the feed wire(red/white) was reading 12.4 with the jeep off, 12.4 at the battery, and 12.4 at the fuse block under the hood (took the fuse out and read voltage there). The headlight was at 10.8 with the jeep off. turned the jeep on and got 11.6 at the headlight. 13.5 at red/white wire

 

None of that sounds wrong to me.

The stock headlights barely have enough power and wattage anyway, I mean the harness is 18 gauge wire...

I'd defiantly recommend a new set up that can be done for $100 or less.

 

55w/60 H-4 bulbs with Autopal housings & a relay are better for most applications and the bulb life is almost twice as long. Plus, with 80w (I don't see an 80 listed only 90w/100 or 130) if you drive in snow or fog you will be dead in the water because you will never see the road through the glare.

 

I have to agree the factory harness is more likely than the switch to be the source of the voltage drop noted.

 

the harness gets it's voltage from the switch, so if the voltage is not leaving the switch it's not the harness--same voltage leaving switch as at headlight. no voltage drop through the harness. The switch must have resistance in the contacts, so I think I'll change it. It's only $20. I will post results.

 

Is the switch running hot? They do run right at their design limits and tend to fail by showing increasing resistance. So does the connector, which might be worth looking at too.
Agreed the harness is under engineered at best, replacing it with a relay setup makes a noticeable difference. (and stops the switch failures too)

 

the switch is not hot. I tried to spray some contact cleaner in it, and run the switch in and out, but no difference. I also tried to wiggle the wires going into the connector.

 

Put a supplemental harness on it before beating your head against a wall any more.

The switches are a bit weak to begin with and the factory wiring is woefully undersized and uses no relay. Trying to get the necessary voltage to your lamps using the factory wiring is like polishing a turd. It's never gonna shine and will stink anyway.

$35 to $50 or so for the harness and can be installed in half hour.

http://www.ebay.com/itm/CERAMIC-H4-HEADLIGHT-RELAY-WIRING-HARNESS-2-HEADLAMP-LIGHT-BULB-SOCKET-PLUGS-7X6-/330813121438?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item4d05ffa39e
http://www.eautoworks.com/Putco-H4--...s-PRD7540.aspx


And here's how to install whichever harness you may choose:

Cruiser’s Headlight Upgrade Harness Instructions
　
It's easy to install a supplemental headlight harness.

From the factory, the voltage to the headlight bulbs travels from the battery, inside the cabin, to the headlamp switch, and then back out to the lamps via undersized wire. 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 30% brighter headlamps and headlight switches that don't melt and burn out.
　
　
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 12/10/2012

 

thanks for the info

 

I will take everyones advice and change the harness. thanks

 

Good on taking the advise. But, you're not "changing" a harness. You're "adding" one.

Here's a step by step write-up with photos from one of our buddies right here on CF:



https://www.cherokeeforum.com/f59/my-h4-upgrade-114440/