still getting REDUCED ENGINE POWER message
so if I'm getting this right, you only have this problem when you turn the stereo on, correct?
What it sounds like to me is you have a short someplace that when you turn the radio on it starts grounding out really badly. Here is a test to do - turn the car off, and test the voltage at the battery. Then turn the key to accessory, and test the voltage again. Then turn the radio on and test the voltage again. If the voltage drops a lot when you turn the radio on, it is most definitely related to that system.
Next step - disconnect the power to the amplifier(s). Turn the radio on. Does it still drop down a lot or not? If so, then there is an issue with the HU, either internally or one of the connections to it. If not, then there is a problem with the amp(s). If you have more than one amp, hook up one at a time until you have the problem again. Then disconnect all the amps except the one that caused the problem. If you still have the problem, you know it is related to that amp. Check ALL the connections to it. If the connections are all good then the amp is most likely shorting out inside someplace.
Hope this helps!






