My friend borrowed my '89 full sized blazed to haul his boat to the lake.......well he forgot his trolling battery, so he "borrowed" mine for the baot. No big deal. As long as he leaves enough juice to start the blazer when he's done. Well, when he put the battery back in the truck, he hooked it up backwards. Yep pos to neg, and neg to pos. He said he heard a pop and the alternator started smoking. I went to the lake where he was at and confirmed a FRIED alternator. Also I found the ECM-B fuse blown under the dash. Looking at the diagrams, it powers both the ECM and the fuel pump. Which component would most likely be the problem? I looked at just about every inch or wiring and saw no heat damage at all. By the way, my friend is $$LOADED$$ and would replace the entire truck if I told him it was junk.....LOL. He has already given me $200 to replace the alternator and told me to let him know what it costs to fix it.

 

Get a new truck! hahaha nah should just beable to replace the alt and battery and the fuse and you should be good to go. The fuses are the for just that reason, they are protecting the computer and all the other stuff that would have been fried by doing that. Should just be a simple alt swap and you should be good to go.

 

well.. a fuse isn't to protect reverse polarity it's to protect from too much current... now if they put what's called a crowbar circuit in the ECU you'll be fine.. that's meant for protecting against reverse polarity... it'll basically short the power wires causing the fuse to pop if you hook up the power backwards. So if these things have a crowbar circuit in them then yeah.. you'll be fine... if not... you might have blown some caps and maybe a couple other components in the ECU. Best thing to do is replace that alternator and try out EVERYTHING in the truck and see what don't work...biggest thing I'd be worried about is that ECU myself though

 

UPDATE!!!!

I replaced the fuse, but it kept blowing......I disconnected the ECU and tried a new fuse. It didn't blow. I replaced the ECU ($75) this morning and that seemed to fix the fuse blowing. Now I can crank it, but not getting any gas. I can hear the injectors firing, but no go juice. I checked out the fuel pump relay and it is good. I disconnected the pump at the tank and I am getting voltage to the plug. Looks like I'll be dropping the tank to see if it might be the pump itself. Fortunately, I replaced the distributor a few months ago and saved the ignition module, so I have a known good one in the garage. Anyone see anything I may have missed????