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Discussion Starter #1
I just acquired an 86' SVO that the previous owner gave up on after putting the battery in backwards. It is getting no power to anything, battery is in correctly now lol, and it looks like something got fried. When you turn the key nothing happens, no power to anything, and it won't crank using a hand trigger. I immediately suspected the starter solenoid, however that doesn't quite explain why nothing gets any power at all right? The main fusable link from the solenoid to the alternator is intact. I bypassed the solenoid all together and no power gets out of the alternator to the rest of the car it seems, but I wanted to ask second opinions before I throw money at anything.
 

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Check the inline fuse links also. I had one burn on my old 86gt and gave me very similar issues you are having. They are located on the left fender apron. Svo and gt should have similar body harnesses.
 

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Fusible link (large wire) from battery to fuse panel. Designed to "melt" inside its insulation.
 

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Discussion Starter #6
Well, so far I checked all fuses and relays and they were fine, so I took my multimeter and put it in circuit testing mode with audible beep when circuit is completed, and tapped one end to negative post of battery and other to the starter solenoid posts with the battery disconnected and it beeped. Took off one wire and tested it at a time, and it looks like I have a short to ground on three of the wires connecting to the relay, the main harness wire, the one to the computer and another I'm not sure of, maybe to the fuse box for power windows etc.

So looks like a melted wire/wires in those harnesses are shorted to ground? I tested in ohms too, and it is open loop on all the rest of the wires on the starter solenoid but it is picking up low ohms reading/zero on the wires that are suspected to be shorted out.

I'll keep looking at wires, look for any obvious melted damaged stuff, test wires to see where the short or break is.
 

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Discussion Starter #7
So far I've found and fixed two problems....

first was the starter was loose, the power wire running to the starter was loose and shorting out as well. PO said it had a rod knock, come to find out it was a loose starter with two bolts missing and last one only a few threads from the starter falling right out. Fixed that.

Next, left multimeter on continuity mode so that it beeped on that shorted wire that leads to the main power in the fuse panel, and I started wiggling and moving every single wire along the main harness, looking for where it could be shorted to ground, and I smelled for any sign of melted or burnt wires or anything out of the normal. Found nothing.

I pulled down the fuse box from under the dash and examined it, every fuse intact, wires all intact, and thats when I traced a few up to the ignition switch. I unplugged the ignition switch and the beeping of the continuity tester suddenly stopped. I had found the area of the problem. Suddenly the ignition switch fell apart into pieces, inside it was a shorted mess of blackened plastic and copper. Yup, its fried!

So it will be a while in this weather for me to replace it and get everything back together to see if I fixed the problem. Figured I'd give this update for anyone curious.
 

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Discussion Starter #8
Replaced ignition switch, continuity test still showed a short to ground, so testing each individual wire from the ignition switch harness showed a black with green stripe wire is the culprit, it is the only wire on the harness that is shorted. I do not know what it does and I'm searching for color coded wire diagrams online now. I find its purpose and where it runs to and I find my problem.
 

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Discussion Starter #9
Thanks to veryuseful.com and TMOSS I found a beautiful color diagram of the ignition switch wiring. Turns out the wire is just for crap like power windows and locks, AC and wipers, so I snipped it for now, at least to get the car running.
 

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I hate electrical gremlins. I am glad you are successfully tracking your problems down.

Sent from my VS980 4G using Tapatalk
 

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Discussion Starter #11
Well, it seems the fuel pump is not working. If I jumper wire it, it will run, so that led me to believe it is a bad ground. I checked fuel pump relay and if I hold it in my hand and turn the ignition key to run I can feel the relay clicking rapidly for a few seconds, and it makes the fuel pump rapidly turn on and off as well. It had 12v and the inertia swith has 12v into and out from it.

I'm following a crank but no start checklist for fuel injected mustangs. I'm doing step by step right now so i don't miss anything. I hope I track the problem down soon.
 

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Discussion Starter #12
I installed a ground wire from chassis to a toggle switch that runs to the tan/green stripe #22 wire from the computer, so now it has ground signal and car runs every time you start the car. This doesn't fix the original problem and is meant as a bypass solution.

Got the car running, took it for a spin, and it went dead a few miles later, battery went down to 7 volts. The alternator is a 3g swap, it is dead as a door nail. Got a new 94-95 mustang alternator ready to drop in soon as I can, hopefully it will be the last thing to fix after the initial disaster of putting a battery in backwards. May this thread serve as a warning and logical means of diagnosing electrical gremlins.
 

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Man I just read this whole thing and props to you man. Have fun with the car!


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