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The ignition wire is powered when the key is in the run or start position. This is because the ignition wire powers
the ignition system (spark plugs, coil) as well as the fuel delivery system (fuel pump, fuel injection computer).
Accessory wires lose power when the key is in the start position to make more current available to the starter motor.
How to find (+)12V ignition with your multimeter:
1. Set to DCV or DC voltage (12V or 20V is fine).
2. Attach the (-) probe of the meter to chassis ground.
3. Probe the wire you suspect of being the ignition wire. The steering
column harness or ignition switch harness is an excellent place to find
this wire.
4. Turn the ignition key switch to the run position. If your meter reads
(+)12V, go to the next step. If it doesn’t, probe another wire.
5. Now turn the key to the start position. The meter display should stay steady, not dropping by more than a
few tenths of a volt. If it drops close to or all the way to zero, go back to Step 3. If it stays steady at (+)12V,
you have found an ignition wire.
The starter wire provides 12V directly to the starter or to a relay controlling the starter. In some vehicles, it is
necessary to power a cold start circuit. A cold start circuit will test exactly like a starter circuit, but it does not
control the starter. Instead, the cold start circuit is used to prime the fuel injection system for starting when the
vehicle is cold.
How to find the starter wire with your multimeter:
1. Set to DCV or DC voltage (12V or 20V is fine).
2. Attach the (-) probe of the meter to chassis ground.
3. Probe the wire you suspect of being the starter wire. The steering
column is an excellent place to find this wire. Remember you do not
need to interrupt the starter at the same point you test it. Hiding
your optional starter kill relay and connections is always recommended.
4. Turn the ignition key switch to the start position. Make sure the car
is not in gear! If your meter reads (+)12V, go to the next step. If it doesn’t, probe another wire.
5. Cut the wire you suspect of being the starter wire.
6. Attempt to start the car. If the starter engages, reconnect it and go back to Step 3. If the starter does not
turn over, you have the right wire.
finding the starter wire
finding the 12V switched ignition wire