Suburban stock HU problems

here is my problem: the HU in my 99 GMC suburban used to work fine. one day it started randomly tuning off. the face of the unit got extremely warm (was told the heat part is normal for suburbans). now the thing doesnt turn on at all. the really wierd part is that the unit does have power (the buttons are backlit and if i hit recal the clock shows) but there is nothing in the display and no sound. when it was cutting in and out i would hear a click that was just like when i usually tun on the radio comming from under the dash on the drivers side (my thought was either a relay or the amp there). any help would be greatly appreciated etrik

Check the power to the radio and the ground. There is a orange wire in the radio's plug. It should be 12 volts battery. There is either a yellow or a green wire right next to it. This is the 12 volt + ignition power wire. The black wire in the plug is ground. If all three of these wires check then, the radio needs servicing.sparky

ok. i replaced the HU with an aftermarket and the same thing happens. it shows there is some sort power, but the actual functions start and stop at random. im getting annoyed. does anyone know what the multimeter should read over the 12v, acc, and ground (im an electrical moron).

On the ground (black wire aftermarket) run a continuity test as well as measure the resistance. The + 12volt constant (yellow aftermarket) should be within 1 volt of the battery at all times. The Switched + 12volt (red aftermarket) should turn on and off with the ignition and should also be within 1 volt of the battery.

And check for intermittent shorts on all other wires. Disconnect all wires other than power, ground, ignition, recheck. If the problem exists with only these 3 wires hooked up, look into a new ground and verify the voltage on the power and ignition line. Next start hooking speaker wires up one at a time and check operation after each wire is hooked up. Top Secret, I can tell you but then my wife will kill me.

It sounds as though you have a problem with the ignition power to the radio. Check the radio fuse #17 in the fuse box at the left end of the dash. Wiggle the fuse around as it may be the contacts in the fuse box. This circuit is also controlled by the BCM to keep the radio and other accessories alive after the key is turned off until a door is opened. If you don't care about the retained accessory power, then run a fuse off the thick brown wire in the ignition switch harness and use this to power the ignition wire of your radio.sparky