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o o b b t t a a i i n n i i n n g g c c o o n n s s t t a a n n t t 1 1 2 2 V V
We recommend two possible sources for 12V constant: The (+) terminal of the battery, or the constant 12V supply to
the ignition switch. Always install a fuse within 12 inches of this connection. If the fuse will also be powering other
circuits, such as door locks, a power window module, or a Nite-Lite® headlight control system, fuse accordingly.
I I M M P P O O R R T T A A N N T T ! ! Do not remove the fuse holder on the red wire. It ensures that the control module
has its own fuse, of the proper value, regardless of how many accessories are added to the main
power feed.
f f i i n n d d i i n n g g t t h h e e 1 1 2 2 V V s s w w i i t t c c h h e e d d i i g g n n i i t t i i o o n n w w i i r r e e
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.
H H o o w w t t o o f f i i n n d d ( ( + + ) ) 1 1 2 2 V V i i g g n n i i t t i i o o n n w w i i t t h h y y o o u u r r m m u u l l t t i i m m e e t t e e r r : :
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 ignition wire.
f f i i n n d d i i n n g g t t h h e e s s t t a a r r t t e e r r w w i i r r e e
The starter wire provides 12V directly to the starter or to a relay controlling 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
© 2005 Directed Electronics—all rights reserved
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