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Wiring Diagram Help: Ignition Switch

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For the life of me I have such a hard time reading this portion of the wiring diagram.

 

I'm trying to understand what the "Y" yellow wire does on the 63M plug. Reading this, it appears to me that (B,S) in the start block of the ignition switch grid only has power going to the "Y" wire when you start the car? Then no power through it. Is this correct?

 

Tracing the "Y" wire around it looks to feed: Starter, Antenna timer, and most importantly the ECU. Curious if anyone knows why the ECU would only want power once at start up?

 

300ZX_Power_Route.jpg

Edited by JSM

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after a long talk with my brother about redoing the wiring in my car, we spent some time about the ign of the car and its relation to the ecu. what we came up with is that the ecu does not want to be on sending signals to objects like the injectors until the car is on, so that your key and be on the on position without flooding the engine with fuel. once the key has been flipped to start, then the ecu can send a signal to the injectors and bring on the fuel. Might be completely wrong about this, or just be irreverent to the question at hand, but just seemed like the one i just got talking to my brother about 10 min ago, lol.

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The diagram above is from an 86 300zx Turbo. What is interesting is it's input on + voltage. It has 5 sources going into it. 2 from the EFI Relay, 2 from the Ignition relay (Fuel Pump and Coil) and 1 from the Starter switch.

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The 280Zs have an ECU controlled fuel enrichment when starting, described in the FSM. I assume that it adds injector open duration. Maybe the 300ZXs have the same feature.

Edited by NewZed

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well after retyping this about 7 times, im going back and forth about it. Most of me says the y wire is only active for a moment, then the other part of me is saying that its on once the car is running, due to the fact that power would have to be either cut from the antenna to start its timer, or sent to it again to set off some what of a click to the timer(first power click rises it, second moves it to lower) im not really the best person to ask that question unless im staring at my colored wire diagram for a while tracing everything. Someone else is probably more fit to fully answer this question for you than me. Seems to me that the answer is in the ign switch part of the diagram, i just cant remember what means what with the dots :( ... Sorry JSM

its almost 12 here so my brain has been trying to shut down for a while now XP

Edited by bthomp

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To answer your original question, the yellow wire is energized only during starting. I'm not too familiar with the particular FI system, but as NewZed alludes to, it may have something to do with cold start enrichments.

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