Hey there I've got an 89 blazer with the 4.3. So here's the problem it'll only start when your boosting it off another car(Obviously the battery is shot) but if you turn on any of the lights or put it in drive it instantly dies. I'm not a master mechanic or anything but I'm thinking its an alternator issue. I have an alternator off a 3.1 v6 just sitting around would I be able to swap them out its off a 96. Hoping someone could help me out.

 

I dont know if the other alternator will help but you could get the one on the blazer tested at your local auto parts

you just need to remove it and bring it to a auto parts

 

The way you find out if parts from one car will fit another is go to Rockauto.com Find the part on one of the cars and click the part #. It will give you the other applications part will fit

Otherwise look up each car and write them down.

However, in the case of Alts and Starters .. if they look the same they probably swap.
If they dont look the same... and your two dont.. they probably wont swap.

Why do I think they dont look the same? I looked on Rockauto