Nissan Repair: aftermarket radio cuts out, ohm load, factory speakers

Question
hello Von.  i installed an aftermarket Sony Xr-c5100 AM/FM/cassette radio with changer controls in my 94 Quest GXE.  after playing for about 15 minutes the radio cuts out and all i hear is static almost like hissing from the speakers then it comes back on and then cuts out again and again each time playing the music less.  i pulled the radio and it is HOT.  i ohmed out the factory 5 x 7's in the van and they read around 5.5 ohms.  i know that car speakers are supposed to be 4 ohm.  are these speakers designed for a 6 ohm load for the factory amplifier?  would the 6-ohm load on a radio that should have a 4-ohm load per channel cause this cutting in and out of my music.  when i bench tested the radio i had it all the way up with 4- ohm speakers and it never got that hot.  i'm curious as to if i replace the factory speakers with aftermarket 5 x 7's if my issue will be resolved, or if its overheating because there is not as much ventilation when its installed in the van's factory radio location.  please let me know if you can help me out.  thank you again.

Answer
Dave,

Nissan uses a floating ground and that is the problem.  I it were me I would wire the power, switched ignition and ground to the fuse block and just wire the speakers to the unit and be done with it.  Otherwise, I would get a factory style connector and wire it that way.  In either case you are getting rid of the problems with the factory wiring.  There is nothing wrong with your aftermarket radio.