Hi good day to all, In my '85 xj6 the alternator gage slowly goes up to normal reading, then it drops to zero. After a while it goes back to normal, then to zero again. Sometimes it red lines on the high end for a short time. This seemed to cause a surge in power to my wipers. The battery has never died because of it. Does anyone have any suggestions on where I should start first? I checked the alternator output to the battery , and it read normal. Thanks in advance.

 

the voltage regulator can be the cause.

 

Thanks I'll give that a try. do you know if it is on the alt. or a separate unit

 

Inside the alternator.. If you plan on removing the alternator yorself we can give you some tips. It isn't an especially pleasant job.

Cheers
DD

 

yes the voltage regulator is mounted inside the alternator behind the rear case cover.

you can test in situ per the Service Manual section "Electrical", (see PDF attachment file), but if you have the tools, skill, and patience, and follow the Service Manual instructions, remove the alternator and take it to a shop that can test and repair alternators.

if you are going to work under the front of the car, make sure you install extra support jacks, these cars are extremely heavy at the front and working under them is a dangerous proposition. Safety First.

 

I assume that Jose is correct and that it is probably the voltage regulator inside the alternator. If upon removal and inspection, that is not the issue, it could also potentially be the grounding wire between the alternator and the gage - if there is no proper ground, the alt. will not charge and will read 0. I was considering the possibility that there is a loose ground connection resulting in intermittent charging (causing the up/down readings on your gage) - this might also explain why although there is clearly some issue with your alt., you have not had a "dead" battery yet - just the luck of driving while it cuts in/out enough to charge the battery for your next start up so it's harder to catch the problem.

I would start assuming it is the voltage regulator, put the car up on safe supports as Jose mentioned, pull it and take it to an alt. shop. If they say it all looks good, then it might be time to trace the wiring down.

 

Thanks, I'll try to get to it this weekend. Got plenty of jack supports ,also ramps. if there are any tricks to the process it would be great.

 

I found it easier to just do the basic electrical testing and alt. removal up on jack supports with the front drivers tire removed. Definitely not necessary whatsoever but I tend to get angry/frustrated by hitting my elbows or working in small spaces (great trait for a jag owner, not) so I like to try to make as much room as possible. Other than that removal is basically straightforward. You might look over the diagram and exploded part drawings in the manual I've posted on another thread just to get the parts clear in your mind too before you get under the car. Things are always easier in text than in person.

 

The anti-roll bar will be in your way. Disconnect both end links and remove the LH U-bracket to the frame. The bolts for the u-brackets are best reached from above with a long extension. The anti-roll bar can now be shofted out of the way to allow the alternator to drop out once the mounting bolts and adjuster rod have been removed.

In some cases the alternator also fouls the bid cooler hose on the way down. This is the cooler hose secured to the front of the subframe with a couple small clamps (crused-over with gunk, no doubt). Removing the clamp screws allows the hose to be shifted just a bit to get it out of the way.

Disconnecting the wiring at the back of the alternator can be tricky because there isn't much slack in the wires to allow the alternator to come down very far. You can can lots of slack in 5 minutes by removing the big output wire from the "+" stud on the firewall and the 3-4 pinch clamps that hold the wire to the subframe. This slack allows the alternator to drop downwards enough so you can easily undo the wires


Cheers
DD