Keyed 12v source?
Thread Starter
Staging Lane
Joined: Feb 2019
Posts: 72
Likes: 13
Keyed 12v source? My project is a 65 GMC truck and I'm swapping in an 08 truck (LMG) 5.3 and 4L60e. I had the original engine harness reworked and the builder made a fuse/relay box and all I need to do is the final connections.
The main wires to hook up are : Battery, battery, Keyed 12v, Fan + and fuel pump.
All original wiring was stripped out of the truck and I'm using a Speedway Motors universal wiring kit. I don't have the motor in yet because I thought I'd work on the wiring as much as possible first.
I'm wondering what to use for a keyed 12v source? Do I need to be careful to find a keyed 12v source that has 12v while cranking as well? I've heard some keyed circuits shut off during cranking. Once I know this for sure I'll maybe contact Speedway tech to see if they can suggest a source from their kit.
The main wires to hook up are : Battery, battery, Keyed 12v, Fan + and fuel pump.
All original wiring was stripped out of the truck and I'm using a Speedway Motors universal wiring kit. I don't have the motor in yet because I thought I'd work on the wiring as much as possible first.
I'm wondering what to use for a keyed 12v source? Do I need to be careful to find a keyed 12v source that has 12v while cranking as well? I've heard some keyed circuits shut off during cranking. Once I know this for sure I'll maybe contact Speedway tech to see if they can suggest a source from their kit.
Don't know what fuse panel you have but the circuits fall into three categories, they are: Battery, accessories and ignition. During cranking most circuits are shut down such as heater, etc so that the ignition circuit has better power. If you have a schematic of the board it would be in your interest to identify and mark each of these circuits in case you wanted to add one.
TECH Fanatic
Joined: Nov 2014
Posts: 1,308
Likes: 660
I've also had cars that have a slight break in the ignition power when switching to starter. I have to turn the key fast to avoid having the computers reboot in my vette.
I a previous car (dodge) where this was worse, I installed a capacitor parallel with the ignition circuit that would fill the gap between the ignition and starter positions.
I a previous car (dodge) where this was worse, I installed a capacitor parallel with the ignition circuit that would fill the gap between the ignition and starter positions.
TECH Regular
Joined: Dec 2011
Posts: 420
Likes: 115
You'll want this to be powered in both Run and Start positions. Usually on an older car, a good source is the old power wire to the ignition coil. Just make sure to remove any ballast resistor, if there was one.
Best practice would be to use this old wire as a trigger to energize a relay with a properly sized, fused wire that can then be your new Keyed 12v source.
Best practice would be to use this old wire as a trigger to energize a relay with a properly sized, fused wire that can then be your new Keyed 12v source.
Thread Starter
Staging Lane
Joined: Feb 2019
Posts: 72
Likes: 13
You'll want this to be powered in both Run and Start positions. Usually on an older car, a good source is the old power wire to the ignition coil. Just make sure to remove any ballast resistor, if there was one.
Best practice would be to use this old wire as a trigger to energize a relay with a properly sized, fused wire that can then be your new Keyed 12v source.
Best practice would be to use this old wire as a trigger to energize a relay with a properly sized, fused wire that can then be your new Keyed 12v source.
