Question about wiring ignition

[BB69]

I am in the process of upgrading the electrical on my Corvette. One of the major items is getting a good 12v supply to the HEI. I have been reading diagrams, and I can't see how the ignition gets power in the original Chevy system, or how it is turned off. I have located the original purple ignition wire, and it gets power only in the crank position. So, based on the diagrams on this page http://www.chevyhiperformance.com/te.../148_0312_hot/, I can't see how power would be maintained to the coil. Can someone clarify this for me?



Thanks
Ken

[myclone]

So, based on the diagrams on this page http://www.chevyhiperformance.com/te.../148_0312_hot/, I can't see how power would be maintained to the coil. Can someone clarify this for me?

Thanks
Ken

Based on those diagrams the ign coil wont get power....now whether its a typo on their part or they are omitting part of the circuit for clarity I cant tell you. None the less neither of those circuit schematics will allow the ignition coil to be powered if hooked up as theyre shown.

What I can tell you is that the purple wire, when used on GM stuff, is normally just for the starter selonoid and it only gets power when the key is turned to the "start" position but is unpowered when in "run" (you prolly knew that already).

What you need to do to get power to the coil is find the wire that comes from the ignition switch that stays energized during both the start and run positions of the ignition switch and is de-energized when the switch is turned off or in the accessory position. If you have the wiring schematics for your particular car this wire(s) should be fairly easy to locate and tap in to.

[gmachinz]

David, do you think for voltage drop concerns (if any) it would be a good idea to run a relay for the coil so that it would see a more reliable 12v and thus not have as a high of a load going through the ignition switch? Just a thought-and no intent to highjack the thread. -Jabin

[myclone]

David, do you think for voltage drop concerns (if any) it would be a good idea to run a relay for the coil so that it would see a more reliable 12v and thus not have as a high of a load going through the ignition switch? Just a thought-and no intent to highjack the thread. -Jabin

You could do that but the primary side of most ignitions doesnt really draw a huge amount of current so most any ignition switch should carry the load reliably for decades on end.

The starter selonoid uses a seperate set of contacts from the ignition circuit inside the switch on GM stuff (usually) so the ignition system really isnt affected by the current draw of the starter selonoid.

[MrQuick]

The diagram shown is a general schematic for a starter bypass relay set up. The R terminal shown to feed the ignition is for the resister wire bypass, so the ignition system recieves a full 12v at crank the goes to resisted voltage(6-10v) after key goes into the run position.Voltage was resisted to reduce points burn up.
On your 69 Vette, there should be a yellow wire coming from your starter R terminal and runs to the coil B+. Now if you look at your coil B+ side there should be 3 wires, 1 white furry wire that goes to the bulk head, a yellow from the starter and a black wire that goes to a capaciter on the firewall.
If you need a full 12v, you can go into your bulk head connecter and remove the original B+ feed (furry white or grey wire) and replace it with a 14g wire.The circuit behind that is a full 12v feed(usually a 12g pink wire) from your ignition switch. You will have to rewire your ignition switch to get 12v while cranking, or run the bypass as laid out in the schematic you posted.