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Discussion Starter #101
Hey Tom, guess who :) Quick question, how did you wire your ignition hot wires to your harness? I read this on lt1swap... The PCM also gets 12V+ from a KEY HOT source. This is what 'powers up' the PCM. Its important that this key hot power, along with power to injectors, coils, and so on, STAY HOT when cranking over the engine. Some accessory positions on key switches ARE NOT HOT when cranking. This also includes older vehicles that had POINTS ignition. Even the COIL wire on some of those went dead when cranking. This is because when cranking the coil was boosted to 12v+ through the R terminal on the starter solenoid. After cranking, power was restored to the coil through a resistor, lowering voltage to 6 volts.

Can I use my stock switch? Thanks again for being an amazing guy and a great resource!! Someday I will somehow repay you :)
Yes you can use the stock switch. Look on your fuse block. There is a terminal there that stays hot in start AND run but I cannot remember what it is labeled. Use your Ohm meter and find that wire. You can come off the switch also, it's the same wire, just easier to access it at the fuse block.

The PCM needs a full time hot and the "switched" hot to work...


T,
 

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Got it, makes total sense
Yes you can use the stock switch. Look on your fuse block. There is a terminal there that stays hot in start AND run but I cannot remember what it is labeled. Use your Ohm meter and find that wire. You can come off the switch also, it's the same wire, just easier to access it at the fuse block.

The PCM needs a full time hot and the "switched" hot to work...


T,
 

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Yes you can use the stock switch. Look on your fuse block. There is a terminal there that stays hot in start AND run but I cannot remember what it is labeled. Use your Ohm meter and find that wire. You can come off the switch also, it's the same wire, just easier to access it at the fuse block.

The PCM needs a full time hot and the "switched" hot to work...


T,
Tom,
Does it matter that the stock switch drops power while cranking to the switched 12v terminal or will the pcm make up for that? Thanx
 

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Discussion Starter #104
Tom,
Does it matter that the stock switch drops power while cranking to the switched 12v terminal or will the pcm make up for that? Thanx
Yes it will matter. No the PCM cannot make up for it. What the PCM needs is constant 12 volts to keep the operating system inside running, much like your home computer. It's always active, but in sleep mode while you aren't using your vehicle. The keyed hot wire sends voltage to the circuits for the injectors, coils and other sensors. The computer then pulses the negative wires to operate some, not all, of the sensors...that's the basic premise of the PCM function, much more going on besides that, but you get the idea.....

This is the single most common problem that trips folks up in their swaps causing a no start condition....


T,
 

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Tom do you have a new build in the works?
what happened to the white car?I never see that guy on here?
 

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Thats how i have it, I hot wired it to run the motor before i buttoned everything up but that was with a toggle switch. I have the PCM running a 12v constant hot from the fuse panel and the 12v switched lead from the PCM to the IGN on my key, The thing is when I tested it the IGN cuts out when the key is in the crank position then comes back on in run. Is this the correct way to wire it up or does it need a 12v switched that stays hot when cranking and it run? Thanx

And yeah what Batman said.. What happened to the next build?? aren't you about due :yes:
 

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Discussion Starter #107
Thats how i have it, I hot wired it to run the motor before i buttoned everything up but that was with a toggle switch. I have the PCM running a 12v constant hot from the fuse panel and the 12v switched lead from the PCM to the IGN on my key, The thing is when I tested it the IGN cuts out when the key is in the crank position then comes back on in run. Is this the correct way to wire it up or does it need a 12v switched that stays hot when cranking and it run? Thanx

And yeah what Batman said.. What happened to the next build?? aren't you about due :yes:
It needs to stay hot in start and run when cranking. Use your test light or meter, there is a wire there.

T,
 

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Discussion Starter #108

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Hi Tom, I have reviewed your LS swap and determined we have almost the same set up. That is a very beautiful set-up.:D
 
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