My drivers side headlight went dim a few days ago, thinking it was the bulb on it's way out I replaced both, and they're not the problem (with Sylvania Ultra's as well ). I automatically assumed it was my harness that I built and put back in July/August, so I measured the voltage at both plugs when the Jeep was off and on and got 11.6-11.7 and 13.6-13.7 volts respectively, what else could be the problem if both plugs are getting the same voltage yet one is dimmer then the other?

Anybody?

Is the same bulb dim on high beam too? If it is I would look at the ground circuit for that bulb. Both bulbs ground at the RH (pass) fender under the hood but there are splices between the headlamps so I would think if it was the ground its probably in the wiring between the headlamps.

Ya it's dim on high beam as well, does that mean anything? In my wiring I have each bulb grounded to a bolt that's right above the light.

How would I check this with a multimeter?

Both beams dim, only thing in common is the ground, so as suspected you will probably find a problem with the ground wire, it may be pinched, cut or corroded somewhere.

With a multimeter reading voltage put one probe on the ground pin at the headlamp connector, put the other probe on the battery negative post. With headlamps on, measure voltage (voltage drop), you should not read any voltage, or maybe a very small amount. If voltage is present you have a bad ground circuit. Measuring resistance might show something too, but not always and resistance from ground pin to battery ground post should be less than 5 Ohms. Make sure the ground pin at the headlamp connector is good, clean, not melted and tight too.

I usually try to find wiring problems and fix them but if this seems like its getting over your head, you could always cut the ground wire near the headlamp connector, add wire if necessary and put an eyelet on the end and screw it down to a good piece of metal for a new ground. You could also simulate a good ground with a jumper wire from headlamp connector to ground for testing purpose first too.

I'll double check my ground tomorrow, the ground wire on the back of the plug is already cut and crimped to an eyelet that's bolted in above the headlight. I was messing around with the multimeter when I was checking the voltage the other day and did get a 0 Ohm reading from the plug to my eyelet, not sure if that means anything or not as I got the same reading on both plugs.

I measured the voltage at my ground eyelet with the lights on and got 5.xx volts, so I think it's my ground. Which is weird because the wires solid, the only place it could have gone bad is my butt splice but it's crimped in there pretty well, can't pull it out.

Edit: Cut out my splice yesterday with just enough wire to solder to, doused it in solder, shrink wrapped it, bolted it back up to my ground and it worked! Thanks everyone for your help.