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The Hummer Knowledge Base

PIAA Lights

I didn't install the 4PIAA lamps on the '96 wagon. They have the small lighted (green/off and red/on) switches on the panel. They have been working fine for over 4 months. Now they have become intermittant. They are connected through the main lights in the fact that I must have the main lights on in order to turn the PIAA's on. Now sometimes the face rings on the switches are not lit and the lights do not turn on.

The PIAA switch has 3 wires going to it:

  • ground from a local connection point (i.e. not nec the same as relay ground)
  • output to go to the relays (12V only when switch on (red))
  • 12V input from switched your case the headlight circuit

First, if the ground is bad, your switch will not illuminate. However, the switch will still function. So I doubt this is the problem unless the ground is common with relay which is unlikely unless the relays are inside the cab.

Second, if the output wire is bad, this would not affect the illumination of the switch...only relays. So I doubt this is the problem either.

Finally, the 12V switched power input. If this is bad, the switch will not illuminate nor will the relays work. This is the most likely fault.

You need to check to be sure that it has power when the headlights are on. If you trace back from the swtich, there is a connector that you can probe easily...should be about 18" away from the switch. If you cannot find this, you can just probe directly into the wires themselves. I cannot remember the color codes though but it is easy. With your headlights on, probe each and one of them should be 12V. If none of them are, that's your problem. At some point one of them will splice into the lighting circuit which is most probably the culprit.

If you do have 12V coming out with the headlights on, but not when off, this is working fine. Your switch must be flakey then and you can rig in a replacement easily.

Internally the switch is DPDT micro push button (two position only). If I remember right, it uses two bicolor LEDs through 4 resistors with a ring as a light pipe. Easy to fix if it is bad.

I don't think there is an "normal" installation. I do have the PIAA diagram online if that helps at:


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