94 es300 radio not working

i have a 94 es300 the radio is not working. i have 12 volt constant and ignition power at the harness and good ground tried another radio need help any guesses?

Could you clarify "not working"? Does it turn on but no reception? Nothing at all? Do the radio face lights come on when the dash lights come on? This is a less-common problem so the more info the better.

there is nothing no lights no sound. The customer brought it in origionally with the battery dying we replaced the battery worked fine for a week the cust picked up had the same problem a couple weeks later. we couldn't find anything wrong with it suggested dealer to check wiring. after the customer went to the dealer the radio quit working and now the battery is dying again. oh yeah the dealer couldn't find anything either they just threw another battery in it.

Consistent problems with "dead" batteries tends to point to charging problems with the alternator. My guess is that the diode block and/or voltage regulator has gone bad and is overcharging the battery or causing a short or back voltage in the radio circuit. Also check that there isn't a blown fuse on the back of the radio (some aftermarket units have this). Finally, do a simple load check on the battery by connecting an ammeter between the negative cable and the negative battery post. Check this with the key off to see any draw on the system without charging. DON"T KEEP IT CONNECTED WHEN STARTING THE CAR. Reconnect the battery cable. Hope this helps!