On a recent trip to the shop for annual inspection, the mechanic said I had a bad headlight on my 1986 XJ6 III. The light had been dim for quite a while, but now it is totally dark. We replaced the bulb but had no success in fixing the dead bulb. The high beams work fine as does the other headlight. On the inside dash, the indicator for bad lights/bulbs is illuminated, but I thought I traced it to a rear light (using the procedure for narrowing the suspect bulbs, found in the manual). Is there a separate line feeding each light bulb? Winter is nearly here and my small sports car has way too big of tires and tread design that is great for performance, but lousy for snow traction.

Jim

 

Check the headlight fuses and clean the fuse holders under the bonnet on the driver's side. Each headlight has its own fuse.

 

In the odd event that Coolblu's advice doesn't work ....it almost certainly will....have a good look at the headlight grounds. As I recall you'll find the ground point next to the radiator.

After that, remove the headlight fusebox (easy....one small bolt) and clean all the bullet connectors.

Cheers
DD

 

I have been fighting with this headlight issue, but still having problems. The fuse box has been cleaned as recommended, but I still have a dim low beam on the driver's side. If I measure the voltage to the light with just the low beams on, I reAd 12v. If I turn the high beams on, the voltage drops to 5V. I suspect a possible problem with the headlight relay box, as this is where I am measuring the voltage drop...but still haven't ruled out a grounding issue, as the relay issue sounds like it displays the characteristics of a ground loop, with the low beam feeding back thru the relay to the high beam ground, via the high beam bulb, which acts like a load to the circuit. This might explain it but more diagnostics are needed. Its a real head scratcher!
I am wide open to any suggestions...I'm 30 miles away from the shop and they are at a loss and I'm trying to eliminate potential problems by isolating either voltage in or the ground...but you know how some shops can be when you try to tell them their business. They are great for 99% of the stuff, but weird issues like this sometimes require some advanced troubleshooting techniques. I'm trying to avoid sending it to an electrical shop since it will quickly add a few more hundred to the bill for a probable simple fix. Has anyone had an issue with relays causing problems like this?

Jim

 

The circuit branches off left and right *after* the relay..... so if the problem is just on the left side then the relay itself isn't the problem.

Go ahead and check the grounds. Not much point in thinking about anything else until good grounding is verified

Look for the "S57" wiring diagram in the How-To sticky thread at the top of this section. It illustrates the circuit very clearly. No need to have a electric specialist as the circuit is totally non-exotic.

Cheers
DD

 

The small bolt Doug described was frozen when i was having lighting issues. But, it was easy to sanp the fuse holder out of the holder. Yeah, not good writing, but descriptive, nonetheless. I scrubbed the underside with a stiff little brush and brake cleaner. it was handy, and carb cleaner is just a tad corrosive. Not good enough for real carb cleaning. That EPA thing.

I found my issue in the ground.

But, at times, just rolling the fuses in the cradle restored order.

Carl