Possable ECM? on 1992 GMC Yukon

My 92 Yukon runs well but only after I disconnect the battery and reset the codes. Once i reset the codes it will start and run fine until I turn it off. Then I get an low buzzing sound and no dash lights or anything. I already replaced the ECM and installed my original POM into the new ECM before installation because of this same problem. Any Ideas as to what else could be causing this?

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1 answer
Take it to autozone have them check what codes are coming up, my 94 yukon head light switch had to be replaced bad and shorted contacts inside the swicth from over heating.