Stereo Cuts Out With Other Loads, 1995 Toyota Previa

I installed a JVC stereo in my '95 Previa and have consistently been having it cut out, throw distortion/static through speakers, and displays a "Miswiring" fault on the display *when the car is running and I apply another load* (like touch brake pedal, turn on headlights, etc). This does *not* happen when just playing the stereo off battery only, without the car running. I had the alternator checked yesterday, and AutoZone said it was fine under load. I've checked and rechecked the wires for the Metris 70-1761 aftermarket adapter, with my stock 9-speaker/sub system and all appears in order. The Red "Constant" wire reads a constant 12.85V when on battery only, and rises to 14.66 with the car running. The Gray "Switched Power" wire reads .62V when off, 11.62 when on battery only, and varies from 13.5-14.4V with the car running and various loads. The Brown "Ground" wire seems consistent. I've had this stereo in and out of the dash multiple times, and am so baffled. Would love advice!

Misfiring means that 1 or more channels are shorting. If your car has 9 speaker system I belive you should be using metra 70-8112. I would check that first. The radio may also be fried. If vehicle equipped with factory amp and hooked up incorrectly there's enough voltage to damage radio. Sometimes Toyotas has a visible factory harness that plugged into oem radio but if you look deep in towards the right side there may be another joint.Rocky Verma