12v+ Keyed IGN source that is also hot while cranking - Pontiac GTO Forum
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post #1 of 15 (permalink) Old 02-16-2017, 01:08 PM Thread Starter
 
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12v+ Keyed IGN source that is also hot while cranking

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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post #2 of 15 (permalink) Old 02-16-2017, 05:12 PM Thread Starter
 
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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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post #3 of 15 (permalink) Old 02-16-2017, 07:48 PM
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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-D...FdgegQodUOEB8Q
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post #4 of 15 (permalink) Old 02-17-2017, 10:28 AM Thread Starter
 
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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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post #5 of 15 (permalink) Old 02-17-2017, 05:15 PM
 
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The coil wire should have 12v anytime the key is on & while cranking
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post #6 of 15 (permalink) Old 02-20-2017, 10:15 AM Thread Starter
 
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Huh. The yellow wire right? Mine is only hot while cranking ?
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post #7 of 15 (permalink) Old 02-20-2017, 04:59 PM
 
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Originally Posted by Dealer369 View Post
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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post #8 of 15 (permalink) Old 02-20-2017, 07:53 PM
 
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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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post #9 of 15 (permalink) Old 02-20-2017, 11:26 PM Thread Starter
 
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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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post #10 of 15 (permalink) Old 02-21-2017, 09:17 AM
 
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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.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring

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