Negative dimmer wire

Okay I need to hook up the dimmer wire to get my gauge lights to work but the problem is that there is only a dimmer negative wire and no dimmer positive. I tried to make it work by hooking up the dimmer negative wire to my power wire and it worked but backwards...when the car is running the gauge lights are on but when i turn the headlights on they go off. How/what do I connect the negative dimmer wire to to make the lights work properly? Oh and I drive a 99 mitsubishi eclipse if that matters. its a kenwood head unit

use a relay.  negative dimmer wire to pin 85, 12V positive to pin 86 & 87, output to your gauges or what ever you are hooking up pin 30. pin 87a no connection.

or hookthe negative dimmer up to ground.Cause I'm So white and nerdy...

First Class Certi-fried installer