RWK

I did a v8 conversion and for some reason the alternator is not keeping the battery charged. The battery is brand new and I had the alternator tested they said it was fine too any suggestions? The truck is an 89 s10 went from a 4 cylinder to a v8 305 I can start it and it runs good but the battery goes dead rapidly

G.A.S.

Make sure you didnt blow an inline fuse off the back of the alt to the battery.
Will the engine stay running if you disconnect the neg cable while the engine is running?
Have the battery tested. I have bought them brand new and have had bad ones. thats not uncommon

j cAT

if the battery drains over night you will need a ampmeter and by disconnecting fuses find the circuit that is draining the battery....if the battery is not getting charged with engine running , must read output voltage to battery.......should be 14.25volt range....also if possible have current output of alternator measured on 305 chevy it should be around 60amps with engine running and battery charged, alternator 14.25volts.......to me sounds like glove box light on or radio .....max current drain with all acc. off , key out doors closed is 50ma.....

rhandwor

While you could have a drain this appears to be caused by the engine change.
If the test was talking the alternator to a shop for the test. Use a volt meter and make certain it is putting out around 14.25 at idle with the heater defroster and head lights on. The little indicator light in the dash which lights saying you are not charging excites the field so the alternator is working. They also make a self exciter for delco alternators used on boats. Check all wiring is connected properly a big problem on doing an engine swap. The ammeter can also go bad if you have one. I think it is more likely something wasn't hooked up properly.

j cAT

the field wire connector small wire on alternator is sometimes damaged corroded.......but he has not replied to questions/comments so were guessing