97 Ford Ranger Lighted Gauges

I installed a set of Back lite gauges and I have A lot of feedback when my stero is on. This only happens with my lights on. I tried to use a noise isolated on the power side but it didn't help any. The noise is best described as a loud ringing noise. The I.P.C back lite gauges have a reistat to adjust the Gauge lights. Any suggestions would be much appreciated.

They are aftermarket gauges and I used the parking lamp wire going into the O.E.M cluster. The after market gauges do not have there own external switch. I didn't think there is any other wire I could use/ to turn on the gauges with the lights.

Justin

You can use either one of these wires:

brown or wht/blk wire at the headlight switch and also found low in the drivers kick panel

Thanks for all the info. I figured it out, the rheostat for the gauges was right by my pre-amp line driver. I found that my line driver is bad. If you move it around or squeeze the line driver it starts ringing very loud. the rheostat was just adding to the problem. I took the line driver out and all the noise is gone/plus the alternator whine that i also had and could never figure out. 

Thanks for the help Justin