out of my 87 300tdt.the power amp inside the unit periodically wont shut off and can drain the battery.i know there is a small relay inside which is responsible for switching the power amp on/off and i suspect the problem is in this circuit.has anyone dealt with this issue?

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon