Parking lights and gauges

[cjb5]

Spent some time tonight troubleshooting some electrical issues and wiring my interior lighting. While testing out my footbox lighting I noticed that when I pulled the headlight switch out to turn on the parking lights that the needle on each gauge would jump a bit then the volt gauge would reset and then return to 12v and the fuel gauge would also swing to empty and then back to full. The tank has maybe two gallons in it . If the parking lights are on, I can go through the calibrating process on the fuel gauge but as soon as I turn the parking lights off and then back on the gauge resets itself back to full.

Any ideas why the headlight/parking switch has this effect on gauges? Headlight, parking lights and footwell light all seem to work fine by the way. What am I missing?

[AC Bill]

Very odd?
Is your ignition turned off while this testing is all going on? Your voltage gauge should not read 12 volts, unless your ignition is on, (or it's wired incorrectly), that's why I ask.
Headlights, park lights and interior lights are (usually), powered through an un-switched source. Un-switched meaning your ignition doesn't need to be turned on for them to function. Although the gauge lights are also using a un-switched source, the gauges themselves are powered by a switched source. If you crossed up some wires in your daisy chaining the gauges, perhaps the fuel gauge power, is coming from the same source as your gauge lights? I can see no other way for the fuel gauge to show any reading, unless it is somehow receiving power.

[Jeff Kleiner]

Sounds like the gauges are not well grounded and may be chasing it back through their lighting path.

Jeff