1990 300ZX Automatic Electrical Problem



I have an electrical problem that has stumped the local ?Z? experts. The car is a 1990 300zx automatic. The problem described below was initially intermittent, occurring once every several months and lasting for about 45 minutes and has finally become a permanent condition. The ?Z? experts apparently tried swapping the CPU and all other related electrical components without success. The car is original except for the engine, which was replaced with a reconditioned one years ago when the crank shaft key sheered, and I suspect that a harness wire in the engine compartment is the issue. I now have the car back in my driveway and I would appreciate any suggestions on where to start troubleshooting.

Here are the symptoms, which used to all start and stop simultaneously.

1. The antilock brake indicator would illuminate

2. The turn signals would not work (move the stem up or down and nothing happens) even though the four way emergency flashers would work.

3. The power steering would drop into failsafe mode. It felt like I lost power steering.

4. The transmission would drop into failsafe mode. From a stop, the engine would rev extremely high before the car would start moving.


Just a guess, but you may have an intermittent gound somewhere. It might take a shop that specializes in electrical problems to track it down. Look at places where the wires flex first. In a car this old that is where problems tend to happen.


The turn signals and e-flashers most likely use the same wiring and bulbs…

The only difference is the e-flasher switch is hot at all times & the turn signal switch is hot only when the ignition is on.

Looks like theres no voltage to the turn signal switch. Figure out why & the other problems should also go away

Got a GOOD set of wiring diagrams?


I’ve got the service manual that includes wiring diagrams. I was focusing on a common ground or signal as the source but I’ll check the 12V side of the turn signal assembly. I’ll also look into a local shop that specializes in electrical problems.



Take a look at the power distribution section of your wiring diagrams. Do all the items that are not working get voltage from the same pin of the ignition switch?

If they do, you need to test the ignition switch.

Example, the factory wiring diagrams for my 97 Explorer show voltage from battery to ignition switch on pin 37 of the ignition switch.

Voltage from ignition switch to fuses 18 22 & 26 is from pin 687 of the ignition switch.

These fuses power the transmission control switch/rear window defrost/heat & AC controls & turn signal flasher

If none of these items were working, I’d test for continuity between pins
37 & 687 of the ignition switch.

Other pins of the ignition switch provide voltage to various other fuses.

Strange that Ford uses 2 & 3 digit numbers for an ignition switch with only 8 pins. Go figure.