Hey guys. I've got a 2000 F250 7three. I just put 2 new batteries in it, fully charged. Now when I'm at an idle, the lights pulse with the motor. All the lights. Interior, exterior, everything. What do you guys think it could be? The old batteries were completely dead for about a month, so I'd jump start it and just take it for a quick ride once or twice a week. Any ideas? It's driving me crazy

 

I'm betting running like you did with bad batteries burned something up in the alternator.

Have it checked and if its bad have it rebuilt by a known quality home town type auto electric shop.

Don't buy junk from the box stores!!

 

Sounds as though you may have some A/C Leakage from your Alternator. This can occur when batteries are Weak or are in need of replacement. The Alternator attempts to be at 100% all the time stressing its components.

TEST using DVOM:

DVOM Select "A/C Voltage", Connect RED to (+B (Post on Alternator)) and BLACK (-) (Not the Battery Ground - You'll need to use a known good ground like a Bolt or Ground Strap).

Your reading should be < .5 VAC. Anything higher is an indication of a failing Diode and requires replacing.

More often than not, just the regulator board needs replacing and can be acquired for about $15.