Well it seems that finally I get to ask a question! My 88 XJ-S has developed a low glow overvolt/overcharge lamp presentation! I have checked battery/belt/ etc. and for those of you who know me I kinda know what I am doing but this baffles me. First there is no overcharge and in fact the battery condition gage tends to run below 13 on the instrument but I have had no flat battery and no failures. If I run at night I can see a glow but if I have heat/ac and headlamps on it glows about 1/3 of its possible brightness. The lamp glows at idle and goes off at normal Rpms but not if you add a load! What is interesting is the low battery warning light while functioning does not come on after the usual time after start up. I swear it acts like a generator/ ign warning lamp. I have also checked the grounds to the alt and tapped on the overvolt module relay just for fun. Anyone had this problem? Thanks in advance.

Submitted by rcmaury@bellso… on Mon, 02/08/2010 - 20:34

The overcharge light is nothing more than a light that comes on when there is a higher voltage at the alternator than the battery. As your accessories pick up power at the Alternator/starter/bulkhead connection and not from the battery, that would explain why the light does not glow as much when accessories are turned on. They draw down the voltage on the alternator side of things and the light does not glow as much. Check for grounds and connections on the battery ground. Clean them even if they look good. Remember that there are two ground wires on the engine, one from engine to subframe and one from subframe to body.

Submitted by dwcurtiss@virt… on Mon, 02/08/2010 - 20:15

Hi George,

Kind of sounds like a "Car Talk" puzzler! As simple as it sounds have you checked the alternator under load demand and then no load? Maybe the alternator diode is acting up?

Good luck!

Dwight