87 s10 blazer 2.8l
 

Got a wierd one. Eng runs ok when alternator is unpluged. While runnig, plug alt back in and eng runs rough, stumbles then dies

I would take your alt to a parts store and have it tested.

87 2.8l s10 blzr
 

Alt is new and does charge. Old one charged as well. Thought i had internal short on old alt but eng does same with new one. Short in gauge cluster or ign switch? Only thing i can think of yhat would make eng run poor then die. Havent found any other thread with same senerio. With alt harness conection unpluged eng runs fine. Any one out there with a similar issue?