What have I done?

[CarPainter]

Hey everyone. Newbie alert.

So, I have picked up a fairly clean 85 300ZX. I'm the third owner. the first owner took very good care of the car. He had it serviced regularly, and kept it garaged under a cover. He only put 113,000 miles on it in 27 years. The morning after the second owner purchased the car he finds that the battery is dead. He takes the battery to the local auto parts place and is informed that he needs a new one. He takes his new battery home and installs it in his new car......BACKWARDS!

He figured out that the ECU was fried, so he tracked down a used one, Installed it, and turned the key. It started right up. It was running for about 10 seconds before the windshield wipers started going, followed by the headlights going up and down. Before he got it shut down the wipers were going so fast one blade self-destructed, and a large flash came from under the dash. Then all the smoke drained out.

So now $300 later I'm the owner of a 300ZX project. My almost 16 year old son will tell you that HE is the owner, and I am only the hired help,

Someone should probably pray for me.

[evildky]

While I have no first hand experience with reversing the battery. I'd start by pulling the fuses to the effected circuits. next I'd track down and test any relays associated with these circuits and then test their switches and then the devices, one or more is likely failed.

[CarPainter]

Hey evildky. I've chased down shorts and loose grounds before, but this is a whole new level for me. I tried to start by figuring out what I knew was good, but after awhile decided there wasn't any part of the system I could be positive about.

So, this is what i know so far. I went ahead and pulled the battery the ECC and all the fuses out of the panel. Six were blown. With all the fuses out, and the ignition switch in Acc. or On, there is connectivity across the the battery leads. If I remember right, about 23 ohms. With the key to off, there is no connectivity. There is connectivity across one stereo fuse location, and from the IN side of that fuse to the OUT side of two other fuses, and also connectivity from the OUT side of the stereo fuse to the IN side of eight other fuses.

I've got a buddy that's pretty good with this sort of stuff. I'm hoping he has one of those audible voltage sniffer thingys, and I can con him into coming over for a couple hours this weekend.

I'm going slow and trying to check as many things as I can without applying voltage to the system. If anyone else has Ideas please feel free to chime in.

[evildky]

sounds like you have a pretty good handle on it. Did you disconnect the items/relays on those circuits and see if any of it clears up? It's not likely a wiring issue, it's most likely relays and devices shorted internally. It could still be in the harness but if thats the case it's due to the wire heating up and melting the insulation off, in which case you need a whole new harness.

[CarPainter]

Since I was given the description of a spark and smoke from under the dash. I'm actually thinking harness or more accurately one of the dash sub-harnesses. I was figuring I could repair a section of the harness with some wire, solder and shrink-tube.

[evildky]

There are a couple of harnesses under the dash and they are not small, might be easier to swap the dash harnesses.

[CarPainter]

You're probably right about that. I should have some extra hands this weekend. I'll keep you posted.

[CarPainter]

I guess it's about time for an update.

First off ......WE HAVE A RUNNER!!!!

So, my son and I have been picking away at this thing the last couple weeks. We have removed nearly all of the interior checking relays, sensors and switches as we went. We found one smoking gun and another possible. One of the anti theft cont. boxes under the passenger seat was very burned up, and the taillight sensor, located by the passenger side taillight, had come unclipped and was hanging down. Somehow, water is getting in around the hatch and the way the sensor was hanging allowed it to fill with water. The well that the spare sits in was full of water as well.

After pulling the anti-theft control and the taillight sensor, all the fuses held when the ignition was turned on. We went ahead and put the Engine Control in, and it started right up. I'm hoping we can just forgo replacing the anti-theft controls or just run some jumpers. We'll see.

We'll start reassembling the electrical system and see if everything else is working or not.

Later

[evildky]

So it was a devise failure

Glad you got it figured out.

[CarPainter]

I'm sure we will find more things to sort out but I feel way better about the whole thing after hearing it run. I know there are problems with the wipers and the headlights but at least the fuses are holding and we can work downstream from the fuse panel.

[BadQ45t]

The leak in the rear where the spare tire sits is very common. Is it rusted out???? You can leave it as is, but the danger is it introduces rust into the rest of the car. I had mine cut out and a body shop essentially made a new one of stainless steel and then we used spray on undercoating on it.

Also, you should check the rear hatch seal and see if that is leaking, another very common one.