Hello there iam new to the sight i have a 1989 mazda b2200 2 wheel drive and when ever the headlights come on my alternator stops working and wont charge the battery it is a bran new battery and alternator i also replaced the main fuse wich is 80 amps i cant figure this out if anyone could help that would be great thanks you

 

Electrical problems can be involved when you have hands on, checking this on on-line will be tricky at best. Battery, ok. Alternator, ok. 80amp fuse, if it was bad, truck wouldn't start.

I'm not currently looking at a wire diagram, but it seems there would be nothing to tie the headlights in with the alternator that would cause the alternator to give up.

Have you taken an actual volt reading at the battery, headlights on, running with the RPM up to say 1500?

Also check all your grounds to make sure they are clean and tight.

Does the alternator quit with any other type of load like the blower motor or wipers or is this failure just limited to the headlights?

 

Does the alternator have an external voltage regulator?
I assume it would being an 89 model it may be dying