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I bought a bt iso din for Mack and the stereo comes but no sound any idea y
April 10th, 2019
2 possible issues.
1st  You have a factory amp on the vehicle.  You need to turn it on with the new radio remote power wire on your new radio.  This wire is blue with a white trace.  Hook this to the 2 blues on the BT ISO DIN and this should turn on the factory amp

2nd
You have a ground speakers lead.  Test all the speakers for short to ground.  Do this with a continunity tester or ohm meter.  If any wire of any speaker is grounded the radio will shut off the audio.

Hope this helps