wiring issue

[apslatton]

so I have an 86 300zx, and the car has been down for about a 2 weeks. about 3 months ago, I lost the digital readouts for tach and speedo and about 2 months ago, while driving the car, it would lose power to fuel pump and ign only, while driving down the road. All gauges and lights etc still had power. So we started at fuses, checked all fuses at kick panel, checked all under hood, none blown. so we wiggled the main harness going to the fuse box inside the car and voila, it would start up. well after dealing with this once every few days, it finally wouldn't take the wiggle the harness trick anymore. after pulling up the carpet last weekend and checking the wiring that i could see going to the fuse box for any breaks or bad connections, I just cut a fuse box out of the ONLY 86 300 the parts yard had and wired it up. Car still will not start. Power to all fuses as before. im not quite sure where to go without a complete wiring harness. Though I like my z, it will find its way to a scrap yard before I go through that nightmare...any help would be greatly appreciated.

[apslatton]

oh and I might need to add that this particular z is a gray market vehicle, not a us vehicle...not sure if that helps or hinders, but I do know things may be different between the two.

[G-E]

The digital dash or the powersupply probably toasted some of the contacts or the diodes, they are a known flaw after 25yrs... not a hard fix either generally.

The wiring to the ignition is short, so any breakage in those wires would be very easy to replace as well.

You said it loses power to the pump too, when it does, have you tried turning off the car and putting it into accessory-ON position, do you hear the pump prime?

[apslatton]

no pump unless I pull the box off the relay and hold the metal piece inside it down. my buddy said it was supposed to pulse and to make a jumper wire from fuse box @ fp fuse to the computer, and/or jump 12v to the pin on the computer and see if it fires then. im not sure what to do with it lol

[evildky]

Sound slike your buddy has more experience with mazda, ford, honda or toyota. The nissans relays are standard 4 and 5 pin relays requiring constant signal. So we are talking about the FP relay? Are you getting voltage on the signal side? Ground on the ground side? It's pretty simple to find out what you aren't getting, the trick is finding out why, but once you know what you don't have it's a lot easier than just guessing. checking for voltage at the ecu pinout might be a better option than jumping from it or another source.

Now for a really stupid question, have you checked the ecu for codes?

[apslatton]

yea I checked the fp relay in the passenger door pillar. I had 019-024 not sure if I had volt set right or not. I also checked at ecu wire and it had 12.xx if I recall correctly. he thinks the wire may be bad between fuse box and ecm. makes since but ive checked wires and even tried a new box. no luck.

[G-E]

There's a priming circuit and an operating circuit... the ecu provides a ground for each, not voltage to the pump as your buddy thinks

Download the service manual from the sticky section...