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Discussion Starter · #1 ·
Been working on my new zap project. So when I got it. The starter, ignition switch, and both battery cables were missing. I replaced all those. Drained the tank and replaced all vacuum hoses and plugs and wires. New fluids and is now cranking but no fuel pump working. I bypassed the wiring and got the pump working. So tracked down the fuel pump relay and took it appart all looks very clean. Then read the maf controls the pump for safety. I tore it down and all looks clean and good. I hooked a test light to check for power at the first two posts as the first 2 complete the connection for the pump. With the key on when I put the test light in slot 2 of the wiring side plug the pump kicked on a few times now doesn't. So went looking for other issues. I pulled the ecu and it looks new and has a Nissan remanufactured sticker on it. So doubting its that. I read another forum thread with someone having this issue, someone said it sounded like the ecu didn't have its dedicated ground hooked up. Saying it's one of the two large wires on the firewall. So I go out and look and both of my large red wires are cut with no ends on it. Looking at pics it looks like one of these red wires hooks directly to the ground cable and the other to the positive side. How do you know which goes where? Both wires look the same. Both heavy gauge solid red wires. I hooked each to ground to check for fuel pump operation and still nothing. But very hesitant to hook either up to positive to not fry something.
108554
 

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Use the FSM to check the positive pin from the connector for continuity to one of the red leads check the one of the 35 pin grounds, it should go to the other red lead. then you will know for sure which is which.
 

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Discussion Starter · #3 ·
Thanks that's what I was thinking. I tried following the two wires back to the ecu but got lost where they both go thru the firewall into the main harness under the dash on the drivers side. I looked thru wiring diagrams and see where the negative should be going to the ecu but nothing in the diagram for the other red wire. Unless I'm missing something.
 

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yea forgot it prob should trace back to the ign relay. The ECU gets 12v with ign in the "run" position. The wiring diagram should get you to the right point to check to. OR you could just make sure one of those reds goes to all the ground pins on the 35 pin connector, that is the neg and then you can assume the OTHER red lead has to be the positive. A little be more risky.

On my 75 its pin 10 of the 35 pin connector and it goes to 88a on the ign relay.

hmm actually you should be able to trace from the ign switch to one of the red leads. That would be the positive.
 

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Discussion Starter · #5 ·
Thanks again, Going to work on that tomorrow. So shocking the manufacturer would run the 2 wires together the same gauge and color with no markings one being hooked to positive and one being negative. That baffles me..
 

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Hey I Recently ran into the exact same problem with the previous owner mixing them up. One way is cutting the black tape maybe 1-3 inches back showing 5 wires, some blue, connected to one of the red wires. This will be your negative and the other your postive.

If for some reason you don't want to do that I suggest disconnecting your afm to air filter connecting and putting a stick or pliers into your AFM having it wide open, then turn your key all the way, then put one wire on the negative and one of the positive, if nothing happens switch when both of them are on the correct terminal you will hear your fuel pump screaming.

Hope this helps but I know you said you traced the wires to the ecu, but you didn't notice the 5 wires on one of the reds so I assume you didn't cut the black tape yet Let us know how it goes!

This worked on my 77 so I'm sure it'll work for all ecu powered 280Zs
 
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