GMC VSL 4000, Installation Manual, Page: 8 / 74

NVSL4000
8 - English
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 steer-
ing column harness and ignition switch harness are excellent
places 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 best places to find the door switch wire are:
■
At the pin switch: When testing at the pin switch, check the wire to ensure that it “sees” all the doors. Often,
the passenger switch will cover all the doors even if the driver’s switch will not.
■
In some GM vehicles with isolated door pins, the door pin wires may be located at the body control module.
■
At the dome light: This may not be your best choice if the vehicle has delayed domelight supervision.
Once you have determined the wire color, the easiest place to connect to the wire is often at the kick panel, at
the windshield pillar, or in the running board. When an easy location is not available, running a wire to the dome-
light itself is often the best solution.
How to find a door pin switch trigger wire with your multimeter:
1. Set to DCV or DC voltage (12V or 20V is fine).
2. In most Fords, fasten the (-) probe of the meter to chassis ground. In most other cars, fasten the (+) probe
of your meter to (+)12V constant.
3. Probe the wire you suspect of being the door trigger wire. If the meter reads (+)12V when any door is opened,
you have found a trigger wire.
finding the door pin switch circuit
finding the 12V switched ignition wire