My 86 xj6 shows 12.5 on the volt guage on the dash. should it not be more like 13.5 - 14 ?

 

Those gauges are known for a tendency to read low. Do you have a multimeter to check what the voltage is at the battery while the engine's running?

 

yes , it is reading at 13 . perhaps after driving the car for an hour or so the volts will come up to 14.

 

That's a bit low, yes.

Jaguar did not specify particularly high output alternators for these cars so if your "13" reading is taken with a bit of a load....for example, a/c blowers blowing and headlights on....that might be about as good as it gets.

OTOH, if "13" is all she can muster with low or minimal load, I'd have the alternator and/or battery checked as well as checking all related wiring, cables, and connectors. There have been some cases where the alternator output wire develops excessive resistance.

Cheers
DD

 

Agreed with everything Doug said and just to add, a voltage drop test will tell you how healthy the cable is. With the engine running put one lead at battery positive and the other at the alternator output. Anything more than a few tenths of a volt shown on the motor would indicate a bad cable.