the gen light comes on after about a 1/2 mile of driving any ideas why its not charging the alternator worked before i pulled the motor why isnt it working now?

 

What kind of voltage are you seeing at the battery terminals?

 

running or off?

 

With the truck running you should be able to get a 12 plus volt reading off the alternator wire. This just tells you it's the alternator and not a battery problem.

If you already know the alternator is not working start simple and work your way through it. You know the connection is good and personally I always put some white lithium grease/dielectric grease in all the fittings. You know the grounds are good, this also includes the main engine ground cause that can affect any part of the system at random. When all this is known good you can pull it and have it bench tested and if it comes up bad order a rebuild kit for a fraction of the cost of a new one.

Since you say it happened after changing the motor I would look close at the main engine ground, just a guess though.

 

i painted the block while it was out od you think maybe the grounds just arent making good contact?

 

i know after i built my engine i forgot to tighten them two really small lock nuts on the back of the alternator, easy to miss and will cause it to not charge

 

thanks fella that was the problem i went out and checked those 2 nuts one was tight but the other one was real loose it works like a champ now

 

yep i did that a time or two