I had trouble with the battery draining and not charging with the alternator a month ago. Battery gauge would never rise above the top of the 13. The needle would always stay below the line dividing charge and discharge.

I pulled the alternator and brought it to Autozone who ran it on their test bench and said it was working fine. Car had a yellow top Optima about 6 1/2 years old. I had not had any charging trouble before that and never noticed if the battery gauge read higher or not. I replaced the battery with a red top Optima. I thought problem was resolved. Drove the car on Sunday for the last couple of weeks about 40 minutes each time. Drove the car this morning and it would not turn over the gear reduction starter after I stopped about 20 minutes after start. Just a click when the key turned to start position.


I put a charger on the battery and after seven hours charge, car started right up. So alternator does not seem to be charging. I don't see any lights stuck on and before I start looking for a power drain I would like to confirm that the alternator is charging correctly.


I would like to rule out the Load Dump Module as a cause.


Any ideas on how to test it? How does it actually work?

 

voltage regulator is probably dead, that is how mine passed.

I wouldn't trust the diagnostic skills of an autozone employee too too much

 

The 1990 has a different alternator than the Lucas that has the regulator internal. Only one wire and the wire from the dump module both on the same stud and the main cable.


I ordered a rebuilt unit from XK's in California. The 90 also has the Load Dump Module, which I do not understand how it works.

 

Disconnect it from the alternator and see if the volt meter picks up.

I've never had to deal with a dump module problem personally but I've read where many guys just unplug 'em and forget 'em.




No, not really. I think there's (at least) a big ol' diode in the little box. Never opened one up to look.

Cheers
DD

 

the load dump module is a set of zener diodes on the end of each winding.

It is the morning and I am at school, so no coffee. Please correct me if I am wrong, but that means if just one of the diodes is leaking, you are going to have parasitic draw on the battery.

No idea if the load dump module is still manufactured or if it is cheap. It is better than the voltage regulator though, older XJSs will illuminate dash warning lights at startup because voltage will be a little low at first. The dump module reacts a lot more quickly and is much more effective at idle