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Discussion Starter · #1 ·
I've been trying to search around to see if anyone else is have a similar issue but had no luck. I'm hoping you guys can help me. I just bought a 99 silverado z71 not that long ago and it would seem that some of my interior system won't work unless I have my headlight switch on. So far the unlock side of my door locks wont work and my interior lights don't work unless the switch is on. It has the security light on but the truck runs and drives with no problems but it appears that the ignition has been changed before. What do you guys think?
 

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Sorry I'm in the great white north and it's been to cold to look into it further. But pulled the dash apart today and noticed that someone has put a jumper wire in behind the headlight switch. Anyone know what this is all about. If I disconnect it nothing works and truck won't start but wired back up it works fine when I turn headlights in first.
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So the yellow wire is the jumper. Two additional questions. The orange and light blue wires....do they both come out of the connector on the headlamp switch? And does the jumper just splice in to the orange and light blue wires such that these wires continue on or are either the orange and light blue wires cut such that one end is hanging free and not connected to anything? I will be gone for a few hours and will look into this later today. It sounds like you are able to drive the truck in the mean time so there is time to try ferret this out.
 

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At first look it appears to be jumping power (orange) around the headlamp switch to several interior lights (light blue). Still not sure what effect it is causing. A few questions. Does the dimmer wheel on the switch adjust the dash lights brightness? Does the dome light work and if so does the dome light override button work? And finally do the headlights come on automatically in the automatic position?
 

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flrmatt said:
Sorry I'm in the great white north and it's been to cold to look into it further. But pulled the dash apart today and noticed that someone has put a jumper wire in behind the headlight switch. Anyone know what this is all about. If I disconnect it nothing works and truck won't start but wired back up it works fine when I turn headlights in first.

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Maybe someone did this to make a redneck security system, so that if someone tried to steal the truck, it wouldn't start.

Seeing that you said it looked like someone replaced the ignition cylinder, and the Security light is staying on.

In any case, a circuit is not getting power when it is supposed to, so the jumper is robbing power from somewhere else to feed the circuit.

Hope you get it figured out soon. My Security light has been on for about a year!

CarMech97
 

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Discussion Starter · #9 ·
rollover said:
At first look it appears to be jumping power (orange) around the headlamp switch to several interior lights (light blue). Still not sure what effect it is causing. A few questions. Does the dimmer wheel on the switch adjust the dash lights brightness? Does the dome light work and if so does the dome light override button work? And finally do the headlights come on automatically in the automatic position?
Nothing works in the automatic position. No interior lights at all. And truck goes into security mode and won't start. When I turn the headlight knob to either other position on the switch everything works fine. I have interior lights dimmer switch works and truck will start.

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Discussion Starter · #11 ·
Yes. That is it exactly. It's not really a big deal. Truck runs and drives great otherwise. But seemed a little strange to me. Was just curious if this was a common thing or not. But I'm completely puzzled over this one.

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I have not seen that many headlight switches in my life but I think I can say with some degree of confidence that this is certainly not normal. You mentioned that the ignition switch appears to have been replaced some time before you bought the truck. The following is from the system description for the "Passlock Theft Deterrent;

Passlock is a vehicle theft deterrent system. This system contains a Passlock sensor. The Passlock sensor is part of the ignition lock cylinder assembly. The BCM provides power and ground for the Passlock sensor.

When turning the ignition switch to the start position with the proper key, the Passlock sensor generates an analog voltage signal. This signal is sent through the Passlock detecting circuit. This analog voltage signal is of a specific value to the vehicle, and varies from vehicle to vehicle. When attempting to start the engine, the BCM compares a preset stored analog voltage value with the signal coming from the sensor. Because both values match, the BCM sends a fuel enable password via the Class 2 serial data link to the Powertrain Control Module (PCM) /vehicle control module (VCM) . As a result, the PCM/VCM allows fuel delivery to the engine.

When attempting to start the engine by means other than using the proper key in the ignition switch, the Passlock sensor sends an analog voltage signal of a different value. The BCM compares the preset stored analog voltage value with the signal coming from the sensor. Because both values do not match, the BCM sends a fuel disable password via the Class 2 serial data link to the PCM/VCM. As a result, the PCM/VCM disables the fuel delivery to the engine.

According to the GM replacement procedure there are two separate re-learn procedures that may have to be performed after replacement of the ignition switch. PASSLOCK Reprogramming Auto Learn and Seed and Key (Scan Tool) Learn. Don't know if these were performed or if they would fix the problem with your security light. If the jumper is installed the way you state then the ash tray light and the backlighting on the switches on your doors (windows, door locks, outside mirrors) would always be lit and the battery would drain. It is not at all clear from the drawings how removing that jumper would prevent the truck from starting. I can only guess that somewhere on the truck there is additional jumper(s) or lifted or cut wires that is causing (allowing) this truck to work the way it is. It would be interesting to see what the wiring at the BCM looks like. I think if it was me I wouldn't kick a sleeping dog. As long as it has not burned the truck to the ground and you are happy with it keep driving it. Maybe CarMech97 is correct and this is a redneck security system.
I am sure there is a better man than me on this forum than can figure this out given enough information and time.
 
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