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© 2 0 0 5 D i r e c t e d E l e c t r o n i c s — a l l r i g h t s r e s e r v e d
finding the 12V switched wire
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 avail-
able to the starter motor.
Use the following procedure to find the (+)12V ignition 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 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 does not read
(+)12V, 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 igni-
tion wire.
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