losing voltage, radio won't power up
 

I'm doing a new radio install. Nothing fancy, took out an old Kenwood someone had installed prior to 2005 and replacing with Pioneer digital media player. Keeping speakers the same. 1997 Honda Del Sol. I cut the wires as close as I could to the Kenwood receiver and left the old Kenwood wires connected to the factory wiring harness. Old Kenwood wiring harness had plastic clips connecting each set of speaker wires together with an ID tag. (nice)
I had to run continuous power from my fuse box to the yellow wire on my radio. 12.3 volts at the continuous power source, but as soon as I connect the yellow wire, the voltage drops to 5.8 volts. I have 12.3 volts at the wiring harness on red wire 12 volt ignition and wiring harness ground. I verified I have 12.3 volts to continuous power across chassis ground and ground using the wiring harness ground. What would cause that voltage drop?
Ignition voltage doesn't drop.