Installing Stereo - Wiring Issue

Westend said the Magnetek was a linear power supply with no filtering. They rely on having a good battery connected to filter out the 120 Hz. ripple on the DC voltage. If the battery is dead as Hornnumb said (and I mean VERY dead), it will not act as a filter and you get the buzzing in the stereo. Also if the battery is disconnected, either with a battery disconnect switch or a bad connection to the battery, you will get the same problem. A big clue was you said a light got brighter when you hooked up the stereo. Most of the auto stereos usually have a capacitor or two on the incoming 12v line to eliminate some of the garbage which can ride on a 12v automotive electrical system. I suspect the stereo was acting as a slight filter and raised the average voltage a bit which made the light get brighter. I would check the connections to the battery and make sure the battery switch, if you have one, is on. If everything is good with the connections, check the voltage on the battery with it disconnected. If it's really low (like 4 or 5 volts instead of 12 low), try to charge it with a modern battery charge if you have one and see what happens.

I hope this loooong explanation has help you a bit. In the end though, as others have said, you will be better off replacing the Magnetek electronics. The kit you linked to from Bestconverter looks like it would be an excellent replacement. Get the PD 4655 with the kit if you can.

Good luck and happy camping.

Ken