69 C10 with 2011 LS3

[GbobC10]

Hi Folks,
So I am new to the forum, and looking for help on this project. I have a 69 C10 LWB. It now has a 2011 5.3L and 4L60E trans. The swap is in and drivable. My issue is the stock ignition switch. I have a stock switch in the dash. My ECU needs 12v in the run AND start position on the switch. My switch breaks power from ignition and accessory while engaging the starter solenoid. This kills the ECU. I have been hot wiring the ECU to drive the thing. Stock ECU I think it is an E38. Trans controller is from TCI. This seems like something that must have been worked out before me, how did you do it? Is there a different key switch that doesn't break power? A jumper wire to add someplace?
Looking forward to the solution. Thanks in advance,
Gary G

[LockDoc]

Welcome to the board-

You should be able to connect the ECU power wire to the "Ign unfused" terminal on the stock fuse box. You may want to put an inline fuse in the wire to the ECU circuit if there isn't one now.

LockDoc

[GbobC10]

Wouldn't that cause the ECU to be powered at all times? Would that cause any sort of constant draw on the battery? This is intended as a practical toy and as suck might sit for a couple weeks at a time.
Cheers, G

[LockDoc]

Originally Posted by GbobC10

Wouldn't that cause the ECU to be powered at all times? Would that cause any sort of constant draw on the battery? This is intended as a practical toy and as suck might sit for a couple weeks at a time.
Cheers, G

No, Ign Unfused is only hot when the ignition switch is in the "start" or "run" position.

LockDoc

[GbobC10]

That circuit goes dead when the key goes over to the starter circuit. I don't know if it is supposed to, but it does. It returns to positive 12v when the key returns to the run position. Same happens to the accessory circuit.

[LockDoc]

Originally Posted by GbobC10

That circuit goes dead when the key goes over to the starter circuit. I don't know if it is supposed to, but it does. It returns to positive 12v when the key returns to the run position. Same happens to the accessory circuit.

You must have a problem with your switch or wiring then. That is where I run all of my HEI distributors from.

LockDoc

[GbobC10]

An HEI is a different animal. This is an E38 ECU. Thanks for trying though. I intend to try a jumper from the solenoid trigger to the ignition with a diode in line. That should do it.
Cheers, G

[LockDoc]

Originally Posted by GbobC10

An HEI is a different animal. This is an E38 ECU. Thanks for trying though. I intend to try a jumper from the solenoid trigger to the ignition with a diode in line. That should do it.
Cheers, G

I fully realize that, but my point is that they both require 12 volt power in the start and run positions of the switch. With my HEI power wire plugged into the "Ign Unfused" terminal in the fuse box the truck would not start if there wasn't 12 volts to it in the start position and it would not keep running if there wasn't power to it in the run position. So the "Ign Unfused" terminal has 12 volts to it in the start and run positions of the switch if the switch is working and wired correctly.

That jumper will give you 12 volts in the start position but nothing in the run position so that won't gain you anything.

LockDoc

[GbobC10]

I follow what you are saying, however my system seems to be different. Whether it is a fault in front of the firewall or one of the many mods done to the truck in the past I can not say. I can say the key switch is new, all of it, not just the cylinder. A stock replacement from LMC. I soldered on a new pigtail while I was at it, the old block was pretty crispy in the purple hole. When the purple wire, to the starter solenoid, is energized the pink and brown loose power. Pink is my ignition circuit, brown is the accessory circuit. as soon as the key is released into the run position, pink and brown regain pos 12v.
My thought with the jumper and the diode was to bridge purple to pink with the diode shutting down the back feed that would keep the solenoid open in the run position. The ECU is plugged into the pink via the fuse block.
Cheers, G

[LockDoc]

Originally Posted by GbobC10

I follow what you are saying, however my system seems to be different. Whether it is a fault in front of the firewall or one of the many mods done to the truck in the past I can not say. I can say the key switch is new, all of it, not just the cylinder. A stock replacement from LMC. I soldered on a new pigtail while I was at it, the old block was pretty crispy in the purple hole. When the purple wire, to the starter solenoid, is energized the pink and brown loose power. Pink is my ignition circuit, brown is the accessory circuit. as soon as the key is released into the run position, pink and brown regain pos 12v.
My thought with the jumper and the diode was to bridge purple to pink with the diode shutting down the back feed that would keep the solenoid open in the run position. The ECU is plugged into the pink via the fuse block.
Cheers, G

I guess you would just have to try it. Let us know what you come up with. Sounds like you have a unique problem for sure.... If you put a test light probe into the socket that the 12ga Pink wire connects to on the back of the ignition switch, and it doesn't light when you turn the key to the start and run positions it means your new switch is defective. I have a tested "good" switch I will send you for the postage cost if you want to try it. It would certainly make your life a lot easier if you could just connect your ECU wire to the "Ign Unfused" terminal.

Here are the two color wiring diagrams if they will help.

http://67-72chevytrucks.com/vboard/s...d.php?t=598129

If you click on the links below the pictures in post #1 & #2 it will take you to larger versions of them. You can zoom in and out on the larger ones.

LockDoc

[RManson]

Most aftermarket ECUs require a straight battery connection. I know this isn't an aftermarket deal but I assume it's just as sensitive to voltage drop, etc. I would run the 12V constant and ground wires from the ECU directly to the battery and the 12V switched wire to the key switch. When the 12V switched wire is triggered via the key switch, the ECU will power on and vice versa. This should also overcome your "not switched at cranking" problem as well. Put a big fuse inline between the battery and the ECU if you're worried about it, but if you dig around in your harness, there is probably either a circuit breaker, fuse, or relay already installed that protects the computer. Good luck!