Hi,

My new to me 88 XJS 5.3 seemingly with no rhyme or reason will have a voltage spike. The voltage will go from about 14 on the gauge to pegging at 17+ on the gauge. An episode can last from 1-4 minutes and then randomly with no change in operation of the vehicle or instrumentation will drop to normal again It may do this at low speed/rpm or while on the interstate at 75mph. it can happen 5 times in 20 minutes or disappear for 45 minutes. As it went out for it's first run last night and this morning I have not been able to catch it while idling. I believe it's a voltage regulator. 64k question, where is it? I even have the factory wiring chart that came with the car and I don't seen to see it.

Thanks

 

The voltage regulator would be my first thought as well. You don't see it in the diagrams because it is inside the alternator

Cheers
DD

 

It probably is the regulator, but don't trust the gauge. Try measuring with a meter on the battery terminals, although I appreciate it may not fluctuate when sitting at rest.

Alternatively fit one of the great little Bluetooth devices on the battery and then monitor on the phone app whilst driving.

Good luck

Paul

 

I kinda thought so...