Contour Enthusiasts Group Archives Forums General General Question for electrical guru's

I have underbody lights that i would like to hook up to go on with the existing switch as well as when i un lock the doors. First qusetion is any ideas? Next thing i already tried one way, what i did was go a relay and tried to have that relay activated by the floor lights under the dash, didn't work and here's why. I get it all prepared , everything hooked up except the activation source and power source, both being the light on the drivers side, but before i do i whip out the light electrical tester and test both wires that go to the bulb and here's where it gets confusing. Both the orange and the black have power when the bulb is OFF like a complete circuit would, but when its on only the orange has power. I know my fair share about electronics but this one defeats every rule i know. Any ideas on how to get that realy to work right and possibly and explanation on how the bulbs work and why that "circuit" is like that. Any help is greatly appriciated. Thanx brian

a voltage meter does not read voltage, it reads potential difference. If you want to check the voltage you need to connect the positive lead of the meter to the wire you wish to test and the negative lead to ground, not the other wire.

If the light is on and you put the leads of the meter on the two wires for the bulb, the meter will only read the voltage drop through the bulb.

The positive wire for the light is a good source of power to connect to the "control" pin of a relay. Install an inline fuse for this wire, a 2.5A fuse should be plenty. This way if there is a problem with the relay or the wire it won't knock out the whole circut you tapped into.

For the "power in" pin of the relay I suggest running a wire from a fuse on the fuse panel that has power all the time even when the ignition is off. Or you can connect directly to the battery. Always be sure to install an inline fuse in the wire.

For the "power out" pin of the relay run that wire to the lights you wish to run

and the ground pin of the relay well that should explain itself.

Footwell lights are switched on ground side, not +ve side. With door closed, light off, both sides of bulb will read +12 volts to ground. With light on, only the power side of bulb will read volts, the otherside will be grounded.

I am interpreting your post to mean you want underbody lights to act as puddle lights with door open but also to work as parking lights from headlight switch. To avoid backfeeds in circuitry you will need a diode and/or an isolating relay to be installed depending on car circuits.

I'll keep an eye for a further post if you require additional info/assistance.

Note: without backfeed protection you would have parking lights on with door open and footwell on with parking lights. BTW I believe in your model year dimmer switch was changed to also work footwell lights with door closed, correct?

The other way the underbody's are controlled is by a custom switch. just to for more information.