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Duffy's 1/71 Series 1 240z build


duffymahoney

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Now that you have isolated the wire, disconnect the connectors between the dash harness and engine harness that have a black/white wire and re-test.

If you have taken the dash out of the car during the build, I would wonder if maybe pinched a wire or the wire harness in the dash harness.

Also look for previous owner modifications like a relay for a thermostat-controlled fan.

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18 minutes ago, SteveJ said:

Both black/white and the green white wires show up in wiring diagrams. See attached for the highlighted path.

One black/white goes from the ignition switch to the ballast resistor.

The green/white lands on the other side of the ballast resistor and goes to the tachometer.

The other black/white comes out of the tachometer and goes to the coil positive.

If you think you have a short in the circuit, unplug the 4 wire connector from the back of the tachometer and lift one of the wires off the ballast resistor. You have isolated the wires from one another and can measure resistance to ground at each.

 

 

 

Ignition Circuit.pdf 1.85 MB · 3 downloads

Both the other green and white and other black and white are not shorted. 

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3 minutes ago, SteveJ said:

Now that you have isolated the wire, disconnect the connectors between the dash harness and engine harness that have a black/white wire and re-test.

If you have taken the dash out of the car during the build, I would wonder if maybe pinched a wire or the wire harness in the dash harness.

Also look for previous owner modifications like a relay for a thermostat-controlled fan.

I have never taken the dash out. 
 

I will have to try and find the engine wiring harnesses connector. 

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So the green and white should be a ground? Then the other black and white should be another keyed 12v? Do either share any wire? 
 

I honestly only need a single 12v for my ITB iac. That’s isn’t shorted. So I could abandon the shorted one. 

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No, the green/white is not a ground. Why do you think it might be? You should not dismantle this circuit unless you have another source for a tachometer signal and are not using the 240Z tachometer. I haven't followed your build thread, so I don't know if you are planning on using coil packs. Otherwise, you also need this circuit to provide 12VDC to your coil.

If you don't want your wiring to burn up, I would suggest you use a fused source for the IAC, such as the black/white at the voltage regulator connector. The ignition circuit you are thinking of using is a poor choice for the IAC.

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I have coil on plug. I have the coils positive looping through the back of my stock tach (works perfectly). 
 

the iac uses less then 1 amp. So the wiring is plenty big. It just needs a 12v positive. Then the ecu pulses a ground to it. I can keep in wrapping the tape till I hopefully find the short. Then replace that wiring. So far all the wire looks great. I will also look at behind the dash. Maybe the short is on that side. 

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14 minutes ago, duffymahoney said:

I have coil on plug. I have the coils positive looping through the back of my stock tach (works perfectly). 
 

the iac uses less then 1 amp. So the wiring is plenty big. It just needs a 12v positive. Then the ecu pulses a ground to it. I can keep in wrapping the tape till I hopefully find the short. Then replace that wiring. So far all the wire looks great. I will also look at behind the dash. Maybe the short is on that side. 

Who asked about the IAC current draw? The fuse is to protect the wiring. If you have a short in an unfused circuit, you could have an electrical fire unless you are lucky and take out the fusible link first. I gave you a safer alternative because the wiring is fused on that branch.

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6 hours ago, SteveJ said:

Who asked about the IAC current draw? The fuse is to protect the wiring. If you have a short in an unfused circuit, you could have an electrical fire unless you are lucky and take out the fusible link first. I gave you a safer alternative because the wiring is fused on that branch.

True. The stock coil +  must have no fuse? I honestly don’t know if the wire in using is the coil + or the ignition keyed +. I will have to look for that. 

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For the IAC, if you need a switched source, the black/white at the voltage regulator is a better choice. That wire is electrically the same as the black/white that goes to the ballast resistor. The only thing is that the wire at the VR goes through the fuse box before going out to the VR. If the insulation ever gets damaged, the fuse should give some protection to the rest of the wiring.

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Did you purchase a wiring harness from Haltech? the premium harness runs back through fuses box and relays. 

Did your harness come with two shielded cables (4 wire for cam and crank sensor)? The Cam sensor wire has a switched 12v (red).

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4 hours ago, Blitzed said:

Did you purchase a wiring harness from Haltech? the premium harness runs back through fuses box and relays. 

Did your harness come with two shielded cables (4 wire for cam and crank sensor)? The Cam sensor wire has a switched 12v (red).

I’m using all the stock wires on my haltech. But I have  2 open relay/ fuse spots. So it would work fine, I could run the 12v positive. Honestly I was just trying to be lazy. 

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Understand lazy, that's why I overlaid all Haltech components with the Haltech wiring harness, crank sensor, coolant temp, intake air, coil, injectors, TPS and fuel pump are on a standalone harness / circuit away from the stock harness and fuse box. The only spice into the stock harness is the switched 12v ignition (main ECU connection) at the key harness and stock tach through the Haltech coil wire. 

All stock gauges, components and lights function and operate on the stock harness and stock fuse box. 

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2 minutes ago, duffymahoney said:

I wish there was a way to find where in the harness the short is. Like some sort of heat sensing device. 

I gave you instructions on how to figure out if the short was in the dash harness or engine harness. After that, you look for damage to the harness or evidence of tampering.

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Posted (edited)
29 minutes ago, SteveJ said:

I gave you instructions on how to figure out if the short was in the dash harness or engine harness. After that, you look for damage to the harness or evidence of tampering.

You lost me on that. 
 

But I found my first melted wire. Off the ignition. The black and white, looks to be the ACC circuit. I can smell the burnt wire as well  

22D2B737-DEF7-4CC7-8EC0-E1CCDA15DE44.jpeg

Edited by duffymahoney
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1 minute ago, duffymahoney said:

You lost me on that. 
 

But I found my first melted wire. Off the ignition. The black and white, looks to be the ACC circuit. I can smell the burnt wire as well  

22D2B737-DEF7-4CC7-8EC0-E1CCDA15DE44.jpeg

I told you to disconnect the engine harness from the dash harness and re-test. If you test the engine harness and find no short, you can suspect the short is in the dash harness. 

That black/white certainly got overheated. You are quite possibly correct that it is on the ignition circuit branch out to the ballast resistor. You can verify that, but it takes using a multimeter with long leads. By the way, this can be handy for that purpose: https://www.harborfreight.com/electrical/electrician-s-tools/30-ft-retractable-test-leads-58024.html (Note, they are only designed for low current applications.)

 

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16 minutes ago, duffymahoney said:

I am worried about both the B/W and the W/R wiring. 

 

I can't seem to find a way to disconnect the engine harness from the dash, the schematic seems to show a plug, but I cannot find it.  Googling now. 

Have you looked in the passenger footwell area? If you have a big aftermarket evaporator, it blocks you from easy access.

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Those wires feed fuses, but technically, there is no fuse from the alternator to the ignition coil positive. The wiring diagram shows a fusible link at the alternator, but I don't recall ever seeing that in the wild on a 240Z.  I could have used one there 27 years ago.

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