I have a 1989 F-250 Extended Cab 4x4 7.3 IDI non turbo with the zF 5 speed. The truck is not charging (I put my voltage tester on the batteries while it was running to test) so I am assuming the alternator is bad (I put the two new batteries in the truck charged at 12.6 volts, when running they weren't at 14 or anything like they normally should be and were actually at 11.9 after a start-up and short drive. What amperage alternator do I need for this truck (and what amperage alternator was in these trucks from the factory)? Does my truck have an external or internal voltage regulator from the factory? Any recommendations on which alternator I should get?
Should be an external voltage regulator, it will be mounted on the fender well near the passenger side battery. I'd bring the alternator into someplace like Autozone or Advance that will do free testing for you. You might just need a new regulator, I did this summer when mine stopped charging. Voltage regulator is under $20, so before you buy a new alternator, get the present one checked out. Also, the regulator needs to be well grounded, and so check that, and check that the metal plate its mounted too is actually grounded (its mounted to the plastic fenderwell...)
Oh, and I think the alternator might be 75 amp stock? Although a 100 amp version is also out there.
just get $15-20 ready and hit the salvage yard for 130a 3g alt with built in regulator and have 100a @ idle charge.
search here for more,and search google etc,for all and more you ever wanted to know,and kiss that old 2g and external regulator business bye bye.