Long time not post. Haven't had an issue with my 1984 XJ6 in ages. On way home today I noticed the Volt Gauge reading in the red zone. Dropped to normal 13 v at rest but went straight up into red when moving. Obviously thinking alternator has had it. But wanted to get some suggestions as to what problems might be besides that. The car has been brilliant for years now. Battery isn't particularly old and is the right battery for the car. No warning light on dash. Nothing after market or strange. Ran with current setup for many years with no issue.

 

I can't think of any explanation other than a faulty voltage regulator....which is inside the alternator

Cheers
DD

 

Thanks Doug

So I think I can replace the voltage regulator. They seem to be available. Only question is what is the alternator? So I can get the right voltage regulator. Catalog says PN is JLM76 (superceded by AEU1929). Googling that would lead me to a Lucas 65A I think. I can see the thing in car but it is buried so deep that I can't see any info on it. From the obstructed view it looks like the Lucas. Any chance it might be something else? Underlining here, car is bone stock 84 XJ6 Vanden Plas.

 

Designing and installing the alternator (an electrical device with lots of openings for water to get in) so low in the chassis was a foolhardy thing to do. Of course they will fail in time. One puddle might do it.

 

the original one was a Lucas, for the part number I have no clue.
I replaced the Lucas in my '84 and fitted a GM alternator, for no reason other than to get more electricity. Big disappointment.

The alternator is removed from below, after FIRST disconnecting the battery, then raising the front end, removing the Splash Pan and unbolting the transmission fluid cooling tube to open up space for it to come out after unbolting it from the block brackets. Follow the Service Manual steps. Sometimes the Sway bar has to be disconnected too.

Then take it to any alternator shop for testing and replacing the Regulator, assuming they have the correct regulator which I doubt.

Depending where you are, there is a shop in Monrovia California that rebuilds Lucas alternators, generators, starters, etc.
www.starautoelectric.com