# 12v+ Keyed IGN source that is also hot while cranking



## Dealer369 (Jan 15, 2017)

So I'm looking for a wire that is hot while key is in the "ON" and "START" position while cranking. I did an LS Swap and the computer loses 12v while cranking so it won't start unless wired to 12v constant. I've tried all of the wires at the ignition switch and couldn't find one. Same at the extra fuse block spade connectors. It is a 66 tempest originally with 350 and 3 speed auto. Also it's factory dash wiring. Any ideas? Thanks in advance!


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## Dealer369 (Jan 15, 2017)

Since the purple or yellow wire in the ignition switch are "on" while cranking (purple goes to starter, yellow went to ignition coil) I was thinking I could use a relay system (see photo) but I don't know if having feedback into the pink wire would be an issue. I suppose I could install a diode to prevent this. Any thoughts?


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## 05GTO (Oct 6, 2004)

You could connect a time delayed relay that will apply 12 volts for a few seconds while you start the engine;

https://www.delcity.net/store/Time-...p_kw=&mp_mt=&gclid=CLX2xr6AltICFdgegQodUOEB8Q


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## Dealer369 (Jan 15, 2017)

I suppose that could work, but I guess I'm hoping for something a little less elaborate than that. Last night I connected the yellow and pink wire together to and it ended up working to provide power all the time. I'm just worried about feedback into the circuit.


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## brad900 (Mar 1, 2016)

The coil wire should have 12v anytime the key is on & while cranking


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## Dealer369 (Jan 15, 2017)

Huh. The yellow wire right? Mine is only hot while cranking ?


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## brad900 (Mar 1, 2016)

Dealer369 said:


> Huh. The yellow wire right? Mine is only hot while cranking ?


The positive wire going to the coil has to be 12v with key on & starting, if it was only 12v during starting the car would not run. You will need to look at a wiring diag. to see which wire is for the coil


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## the65gto (Oct 9, 2008)

brad900 said:


> The positive wire going to the coil has to be 12v with key on & starting, if it was only 12v during starting the car would not run. You will need to look at a wiring diag. to see which wire is for the coil


First off, this is a conversion to put a LS in the car. The old wiring had 2 wires feeding the coil, one 12v for starting and one 9-10 volt wire during run. The built in resistance wire dropped 12v to 9-10 volts to keep the points from burning up during normal running. This does not apply any longer because he does not have points. The ignition switch changes the (wires) voltage to the coil when it is in start mode and then run mode. (Terminals 1 and 2 on the ignition switch) Yellow is normally the start wire, pink is the run wire. You have got to bypass the resistance wire since you do not want the engine ignition running on 9-10 volts. A relay seems to be the easiest, however I traced the resistance wire (buried in a bundle) and bypassed it. The wiring info is from a 65 gto wiring diagram, 66 should be the same???


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## Dealer369 (Jan 15, 2017)

Yeah this is the diagram I'm working off of. Rather than just using a kill switch I tapped into the pink wire for 12v+ on run, and spliced in the yellow to have 12v+ on start so my PCM fuse block is connected to two wires and so far it works. But I'm not sure if that's a permanent solution. I stripped most of the wires out of the engine bay harness except purple for the starter and blk and red for the interior power. I'll set up a relay once I get the parts in to see if it works. But I gues since the resistance wire and the other wire lead to the coil anyways I shouldn't be worried about any feedback during cranking? No blown fuses yet at least haha


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## the65gto (Oct 9, 2008)

Dealer369 said:


> Yeah this is the diagram I'm working off of. Rather than just using a kill switch I tapped into the pink wire for 12v+ on run, and spliced in the yellow to have 12v+ on start so my PCM fuse block is connected to two wires and so far it works. But I'm not sure if that's a permanent solution. I stripped most of the wires out of the engine bay harness except purple for the starter and blk and red for the interior power. I'll set up a relay once I get the parts in to see if it works. But I gues since the resistance wire and the other wire lead to the coil anyways I shouldn't be worried about any feedback during cranking? No blown fuses yet at least haha


In theory, the ignition switch should isolate the wires assuming the switch is good, and the harness does not develop a short due to age, rubbing etc. I was able to find the resistance wire by looking for the splice shown in the diagram. The wire itself resembled a piece of shielding, sort of pinkish? in color wrapped in 50+ old electrical tape from the factory. If you haven't yet, pull off the firewall connectors, you will wonder how anything electrical works. :laugh2:


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## Lemans guy (Oct 14, 2014)

Dealer369.... I wired my 66 Lemans with a Relay works fabulous never fails to start runs strong.

I put in a Petronix and wanted a full 12 volts to the coil instead of the ballast reduced 9v for points.

I put a relay on firewall, one screw, ...wire both your 12v start wire and your nine volt braided ballast together, then connect that to the switch terminal at relay.

connect relay power wire to a full 12 volt regulated source. use a 14 gauge wire at least here. Then from relay to + side of the coil another 14 ga wire. Fourth wire grounds the coil.

Just make sure the coil has no built in resistance.

This can all be done from the engine compartment and gives the coil a full charge at start and when running 12v to say 15....Coils are rated 9 to 18v or close, so you get full energy at atart and running.

This works great because the original wire to the coil is 12v then drops to 9v when running to protect points. by just splicing them together, works perfect with a Relay.

The relay will close with about 6v, and it takes even less like 1.5v to keep it closed. Even an old ballast wire will give plenty more and that just closes the relay.

therfore full Power all the time runs great!.....

nothing fancy needed, just don't do it with points!


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## Dealer369 (Jan 15, 2017)

Hey thanks for all the replies! I guess I should have mentioned that my engine fuse block is routed through the firewall into the passenger compartment. And all the wires I'm dealing with are on the interior. But I did just use a 30A relay that is tapped into the wires coming out of my ignition switch and it all works fine!


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## 1968gto421 (Mar 28, 2014)

Lemans guy said:


> Dealer369.... I wired my 66 Lemans with a Relay works fabulous never fails to start runs strong.
> 
> I put in a Petronix and wanted a full 12 volts to the coil instead of the ballast reduced 9v for points.
> 
> ...


Would any diodes be needed in this relay installation? Thanks!


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## Lemans guy (Oct 14, 2014)

1968gto421;

Yes, my fault for not mentioning that Thank you!

I needed the small diode,....it prevents run on after the key is turned off.

It goes in the Brown wire that comes from the alternator and into the harness and then into the firewall. It ultimetly goes to the gen/bat warning light as I recall.

Some cars may have diodes or not need them, I guess it may depend on your alternator and voltage regulator set up.

If you install the relay and the car won't shutoff with key, then you need the diode.

You can disconnect the battery if this happens, or pull the coil wire from dist, or even the connector on the alt to shut it down.

The diode is directional so the stripe has to go one way. real easy though.

Sorry I did not bring that up, but a great full power system if you get it in!


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## rlslavik (Jun 21, 2014)

I have been having issues with a good power source due to an HEI conversion I just installed.
We were discussing the solenoid at the time which has a battery post (connected straight to the battery), and S terminal (the purple wire to the switch) and an unused R terminal.
Your problem is different than mine but along the way PontiacJim stated:

"The "S" post will have the purple "start" wire coming from your ignition switch when you turn the key to fire up your car. The other post, "R" only becomes a hot 12V when the starter is turning/activated - so not a good source to use for constant 12V".

If you are looking for 12v WHILE CRANKING, that R terminal may be what you need.

I did not test and confirm what he said, but I'd bet he is right.

Just passing along info given to me...


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## Toni_EX (Jun 17, 2021)

Lemans guy said:


> 1968gto421;
> 
> Yes, my fault for not mentioning that Thank you!
> 
> ...


Hi what kind of diode Should i use? I have a same problem runs after key is off. 10volts to relay when ignition off and car is still running. When engine is off ign 1 12volts and ign 0 zero volts to relay


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