sslinn

So I recently got an 86 300zx n/a GLL model that has been my grandpa's since it came out. Just a few days ago the battery shorted out on me. I found out the ground to the chassis was corroded and burnt out so I replaced that and now the car starts again, but somehow when it shorted I lost all electrical power to the car. I'm talking no blinkers, no brake lights, no power mirrors, no power brakes, no compass, clock, speedometer, or anything else on the dash or somehow connected to the interior of the car. I checked all the fuses and nothing is blown. Anyone have any ideas? I'm no good with electrical stuff so I'm at a loss. Could one of the fusible links have melted? Did I need to rewire everything? I'm not the greatest with a voltmeter but I have the FSM and am learning slowly. Any hints?

sslinn

Also it has the digital dash still. And everything was working great until the battery shorted on me. I'm lost.

zxguy1986

Welcome. No need to rewire everything. Check out the recent thread ELECTRICAL ISSUES by jamesd83. He accidentally switched his battery cables + for - and fried some stuff. Check out what the guys suggested that he do and see if any of that applies to your situation.

I don't get why a ground cable would melt/degrade/short out without a major electrical problem causing it. And even if it degrades to the point where it is no longer grounding, why would everything else screw up? Unless the car was running when it happened? So some guessing is needed...

Anyway, my suggestion is you should get your alternator/battery system up to charging at 13+ v. and storing normally, get them tested under load for doing that - just to make sure. If you have crappy battery cables & terminals, replace them with better quality, solid connections. Battery too if it's not performing to its max. If alternator is fried, replace that. Output needs to be 13+ volts.

When everything there is solid and working right, you can start chasing down blown fusible links, fuses, relays, etc. There are a lot of 'em. Start with the fusible link at the battery.

Use your manual. Your elec diagrams show all fuses, links, etc. You can get good at using your multimeter to check circuits. It's a good skill to have.

rogerz

Might have fried the power lead to the fusible link box. see if you got 12 v there. did you reground the negative cable to the body. grounding thru the starter not reliable. are your battery cables and terminals in tip top shape? those one size fit all clamp on abortion terminals are trouble on a dark and stormy night waiting to happen. when you say the battery shorted out what do you mean? you didn't have it clamped down and when you went around a corner the positive terminal hit the body????? hAVE YOU had the battery load tested? did you get a new reliable battery???

sslinn

Thanks, yes the car was running when it happened. Sort of a spark spark dead sort of situation. Not really sure what happened. The engine runs fine still so I know it's not the battery terminals. I just replaced both clamps and the wiring to the starter for an unrelated non starting issue. I will be checking the alternator for load as soon as I get off work at a decent time... Thanks for the other thread, I found it and the symptoms seem to be a lot like mine.

sslinn

I regrounded the negative cable to the body with a new wire and leads, the old one was burnt out and corroded pretty heavily. It is not grounded through the starter. I do still have the one size fit all clamps, but those will be replaced soon. I'm not really sure how it shorted out. It must have been something like what you said of the positive terminal hitting the body or the bracket retaining the battery or something. I did have the battery tested, and bought a new one because I didn't really trust the test. They said it was still good but it was leaking and just didn't seem right to me. Both the old battery and the new one will still start the car however.

I have not yet tested the fusible link, looking at the other thread about this same issue it looks like that was the guys problem though so once I make sure my alternator is working that's my first test.

rogerz

if grandad kept the original negative cable there should be a square copper flag that was crimped to the cable about 4-5 inches from the terminal. it is supposed to be bolted with an M8 bolt into a hole that is down and right from the bolt that the clamp uses (at least looking at from the front). the fusible link box is located just forward and outboard of the battery. It should have a 10 gage wire going from the positive terminal to it. with or without an alternator you should have power to/from the fusible link box.

FlyingT

The only way the ground cable could have been "burnt out" is excessive current through it. That could be caused by the ground cable getting smaller and smaller with corrosion, like a small wire with too much current melts. That should be corrected by replacing the wire. If that does not fix the issue, then what must have happened was the positive terminal of the battery was connected to the ground cable, and the negative terminal connected to the positive cable. Or you were jump starting the car and got it backwards. Somehow excessive current got on the ground cable. IE the positive terminal of a battery got on the neg cable. Are you sure you weren't jump starting the car and cross wired the running car/battery wrong? If the battery shorted out internally, it would probably have exploded or melted. That energy stored in the battery has to go somewhere, most likely heat (conservation of energy/matter). If the positive terminal hit the hood or got grounded somehow, the ground cable would be untouched and the battery would have welded itself to the car and probably melted.

If fixing the ground cable does not fix the problem, it had to be wired backwards. I would check all the wiring from the battery to the starter and fusible links.


BTW, I am an electrical engineer.

sslinn

Alright well I still don't know how I broke it in the first place, but I found the problem! It was a fusible link after all. I got to use a multimeter for the first time and everything! Awesome times. I never jump started the car, and I went through the battery wiring that I just replaced (terminal clamps, ground, and on down to the starter solenoid) and it was correct as far as I can tell. I'm gonna say I most likely did what FlyingT said and put the ground on the positive terminal the first time I did it and that's what killed it. I know nothing about electronics so that sounds like my kind of mistake.

Anyways it was the first fusible link in the chain, it says main battery on it but I'm not sure of the actual part number (the thickest one with the black wire). None of the auto stores in this nobody town has a replacement so I will be sautering on a new fusible link wire to complete the circuit. I tested it today without the sauter, just a little wire crimpage from each side of the broken wire, and all of my problems have disappeared. If anyone's interested I can take some pictures or do a write-up etc. as I go if one doesn't already exist yet. It will probably wait until the weekend until I fix it for real and call it safe to drive again.

Thanks for your help everybody.

sslinn

Sorry grey wire, not black wire. For the "main bat" fusible link.

FlyingT

I would still look for the proper fusible link since they are designed to burn out like a fuse and bypassing it with a wire defeats the reason for having one. The wire that was there was designed to burn if a excess amount of current was running through it. The replacement wire is probably not the correct size.

Give Steve a call from the link below. I have been buying take off parts from him for years and he may have what you need.

300zx Parts For You webpage