I'm sure this has been covered enough but when I did a search I couldn't find exactly what i needed, So here we go again. I have a mutt of a truck that consist of a 86 k5 frame, 77 K20 Drivetrain, and a 92 S10 my problem comes from the wiring (which is definately my weak spot). Anyway I am running the stock style Alt. off the 77 K20 I know that is good because I have had it tested. I have the post on the back wired straight to the the battery the fat red wire (which is to the left if you are looking at it from the front) wired to a hot with key and the thiner black wire (which is to the right if you are looking at it from the front) looped around to the post on the back. I know it is charging because the back is magnetic when it is running and I can disconnect the positive battery cable and i stays running. If any of this sounds wrong chime in and help me straighten this part out. The problem is that if I let this truck sit for any amount of time It kills the battery. I have tried searching for a draw with a test light and pulling fuses and found nothing. Any ideas? Is it just wired wrong? or maybe as simple as a bad battery? Thanks in advance and sorry this post is so darn long!