This is actually in a boat. Had a stereo in the boat, worked great in the driveway. It was hooked up to a seperate battery for the stereo and the fish finder. Took the boat out and the steroe started going off and on, powering off and on. Got it home and it didn't power on at all. Figured it was bad (used boat recently bought) so I bought a Pioneer DEH-1900MP. Installed and it wouldn't power on either. Checked voltage and my meter read 10V. Charged the battery and it worked fine. The previous owner had it wired, both the constant + and the switched+ to one battery always powered. I changed the switched to a switched source off the actual boat battery, and left the constant on the aux (fish finder / stereo battery). Worked great in the driveway.
Took the boat out this weekend and at some point tryed the stereo. It worked for about 30 seconds then started powering off and on again.