I notice on my 86 Jag xjs the battery light comes on and off at random on the dash while driving..can someone tell me why. should I be concern... Thanks for your time

 

Usually low charge indicator. A simple volt meter should tell you output. I'm thinking even using the cigarette lighter socket as voltage feed would do

 

The battery light will come on for 2 reasons.

1) If the battery voltage is lower than the alternator voltage.
2) It the alternator voltage is lower than the battery voltage.

Check the charging voltage it should be between 13.8 and 14.4 volts. Battery voltage should be 12.8volts when disconnected.

 

About 25 years ago I had a lady customer that had an XJ-S that had the 'battery' light flicker on/off at times. She brought it to the shop and I told her that the alt and battery were FINE, no fault found.

She wanted a new alternator ANYWAY. So I installed the new alt and she left. A few days later she came back and said it is STILL flickering on/off and wanted the alt replaced under warranty.

The boss told me to replace it and she picked up the car and drove away.

Next day she comes back and says it is STILL flickering.
I asked if it was the battery light and she got angry and told me she has had the car since NEW and knows what light she is talking about!!!!!!!!!!

I asked her to point out what light and she pointed to the RADIATOR (low coolant) light icon.

I told her that was a picture/icon of a RADIATOR and the battery light was over here.

She got real quiet and said 'oh'.

I topped up her coolant level and she drove away.

I never did get paid labor for the warranty alt that was NOT FAULTY.

bob

 

Thanks all.. very informative I will check the Battery output.....