66 tempest LS swap 12v+ while cranking

[dealer369]

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 the spade connectors at the factory fuse block and no luck. Since the purple or yellow wire in the ignition switch are "on" while cranking (purple goes to starter, yellow went to ignition coil) and pink is hot in the on and acc. Position, 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?https://static1.pt-content.com/images/pt/2017/02/80img_0360_8c3d364d32adc892847eda7e5c539-1.jpg

[Richard454]

I'm not familiar with the Tempest wiring...

But looking at your drawing, the devices that are suppose to be off (wipers/ blower motor/radio)during cranking will be on. That takes power from where it's needed - the starter- as you do need the wipers running while trying to to crank your car. FWIW- I'm familiar w/ later GM- and from the factory anything that is powered by the ignition when it's in the acc position - is not powered during start.

Richard
137730

[cpd004]

I've never looked into a Tempest, but most GM car's I've dealt with provide 12v to the pink wire during cranking and run positions. Maybe something is different, but is it possible that the switch is bad? Did it run before the swap?

[dhutton]

Pink wire is hot while cranking as above.

Don

[pist0lpete]

Not sure if it's the same, but on my 67 chevelle the hot while cranking wire was the only fabric insulation white wire under the hood.

[chpr1972]

coming out of the firewall is a funky looking wire that is a resistor wire. What you need to do is find that wire and solder a wire as the same gauge in it's place and run it to the hot side of the coil. On these cars the original wires was a hot wire at 12v to start and a resistor wire to run the coil so the points did not burn up. look for a black and yellow stripe wire and a white orn. &ppl. cr. tr. wire[thats what the 66 manual calls it]. test lite the firewall connector and check for the terminal that has power when cranking.

[chpr1972]

coming out of the firewall is a funky looking wire that is a resistor wire. What you need to do is find that wire and solder a wire as the same gauge in it's place and run it to the hot side of the coil. On these cars the original wires was a hot wire at 12v to start and a resistor wire to run the coil so the points did not burn up. look for a black and yellow stripe wire and a white orn. &ppl. cr. tr. wire[thats what the 66 manual calls it]. test lite the firewall connector and check for the terminal that has power when cranking. That funky looking white wire is a ballast resistor wire and if you are running electronic ignition you are not getting a full 12v to the coil