1990 GMC Jimmy s15 4.3l 4wd
I’m really confused as to what the issue could be, I got a new battery, replaced the positive and negative battery cables. How should I troubleshoot this?

 

i would start by checking for spark and fuel pressure. this will help point you in the direction you need to go

 

yeah that was the next thing I was going to do, but I don’t understand why the headlights and taillights (except brake lights work) won’t turn on. I literally had just replaced one of the headlights right before this happened.

 

i cant see it being related to your no-start, but check all fuses. possibly you shorted something out and blew the headlight fuse. (i say check them all because you couldve blown multiple fuses and another one could be keeping you from getting fuel or spark

is your security light flashing? if it is this points to an issue with the security system which could keep the truck from starting. also possible it keeps the lights from coming on, though i dont know about that

 

update: So I checked all the fuses, only the horn fuse was blown (BTW the horn stopped working a week prior to not being able to turn over) but I changed the fuse & still doesn’t work. I also noticed the PWR ACC fuse box slot said 30a but only had a 15a fuse in it (still didn’t change anything once I put a 30a fuse). I also got a new relay (cause they only had one but going to get another tomorrow) because I couldn’t tell which one was which with regards to the two relays attached to each other right above driving column in the top right of engine bay. BUT I did unscrew the wiring harness’ fuse box connector located underneath the relays, in the far right of engine bay, and there was so much crud all in connector inputs & even coming out the connector in between the wires (which is in the photos) and I cleaned the crap outa those dirty input connectors for fuse box, along with each terminal on the distributor & the spark plug wires, ignition coil terminal, but I haven’t taken off the distributor cap and cleaned the inside yet. Oh and I replaced the entire negative wire going from the engine block near temp coolant sensor on top/center of engine, going to the battery (along with the grounding wire), and also the positive wire going to the starter solenoid terminal (along with the wire going to the back of alternator). Personally I feel it is probable the fuel pump because the previous owner had broken his key he told me and was just leaving the broken key inside the ignition slot on the steering column for a couple months before he found spare key and sold it to me; and I’m just finding out now that the fuel pump stays engaged even just with the key in the slot without turning the key at all, so probably wore out fuel pump. I know next question will be “well do you hear the pump running when you first insert the key?” And the problem is I’ve never really heard the pump run when I first put in the key or literally anything since I’ve had the car, even when it was running fine. Anyways, I’m just going to keep plugging away, troubleshooting everything, please any and all suggestions extremely welcome!!!

 

So I see you’ve don a ton of work searching for a problem, but have you checked for both fuel and spark yet as I recommended to begin with? If you haven’t done this yet, you’re just kind of aimlessly testing tons of different things hoping to stumble upon the issue.

Take the guesswork out of it. Test to make sure you are getting spark. Check your fuel pressure. Forget trying to hear the pump, do a proper fuel pressure test. Checking these 2 simple things will narrow down your search for the issue by ruling a bunch of things out and point you in the right direction. Without testing for these two things first, you’ll just continue to spend a ton of time messing with things that more than likely have nothing to do with your actual issue. Not saying that cleaning your terminals and grounds is a bad idea, just that you should find your actual issue first and then go back and clean things up once you’re up and running again

 

Yeah I guess I forgot to mention that I tested for spark and I’m getting spark, I only checked the first spark plug but didn’t feel it necessary to test them all (maybe I should). I’m going to test the fuel pressure today, what’s the best way to go about handling that? I’d also like to mention that the last time it drove, upon cranking the ignition I did notice that it seemed to either be misfiring or something else which made the car vibrate and bump, sounding very strange at first when it was in park, but as soon as I put it in drive & accelerated it was then back to normal (it appeared). And ever since then it hasn’t started, except for 2-3 times when I tried and it successfully fired up and I would keep trying to tap the accelerator pedal until it seemed to be okay to idle on it own, and then after 30 seconds of that it would turn off.

 

These connectors look melted. On the picture the top right of the large female connectors is definitively melted. On this 6 connectors only the tongue of one pin is still visible the remaining have vanished. If the heat at the connector got to that point and you have so much crud in them IMHO it would be wise to check the whole wiring.
Also check the wires themselves at the crimped-on connector pins. Are the copper strands black/dark? What is the resistance of the wires through the connector?

For once I'm going against the advice of the previous posters. I'd suggest to go after that wiring issue first. The back of that burnt connector may have pins which are no longer connecting (upper right connector seems to be missing the tongues of the female pins) and even shorting or still heating up as soon as powered. Might need electrical diagram to properly troubleshoot. There are IMHO pins missing and that connector including the wiring may pose a fire danger.

What could seem to be unrelated (headlights - wrong fuses) might point to a wiring problem.
We have seen so many problems with the electrical wiring where some jury-rigged stuff has been put into the Blazer's. Also have a good look for repairs in the wiring, added wires, jump-wires (bypassing connectors or supplying some stuff directly).

If going after the fuel and spark first I would strongly suggest to also check ignition timing. Still there are too many possibilities that a messed up wiring can make the Blazer behave like this. May want to have a look at this:
https://www.rockauto.com/en/moreinfo...=9550308&jsn=3

 

So finally figured out the issue. I cleaned up those connections so they look insanely better and it was cause I had a bad computer, so I got a new one and all good!