Aftermarket radio weirdness. Turns off at 5 mph.

[PLP]

As the title says.

The story.
I have been dealing with not the best radio install... I had to redo wiring (speakers were either not connected or wires were "twisted around the post"). In addition channels were swapped.
Anyway, I sorted it out, speakers are now soldered, no more loose connections.
Wiring (power) was also "twisted", not crimped or soldered. Got this done.

Now, the OEM wiring has a nice thick Red (with blue?) constant power, right? That is the +12 V. Then, there should be power from ignition.
I found one wire that would do that as it was hot when the ignition switch was turned on and it would be dead when the key was pulled out.

All good, right?

Not so much.
Radio constantly turns off (I checked it several times) the moment speed drops to 5 mph. It is not RPM, it is not me doing anything. I can gently coast down to a stop and dead at 5 mph (or very close) radio cuts out. Then it comes back on.
Not sure what happens when I start driving, though.

I have seen weird things... but why this one?


EDIT.

More testing.
There is something with 5 mph and this HOT when ignition on wire.

It will loose voltage when going reverse, it will drop signal when going from stop.
Basically anytime it hits 5 mph, the signal is lost.
I am puzzled.

[SCCA_AX]

Is there a fuse inline on the power or turn-on lead?

I had a similar problem on another car a while back and I popped the "fuse" holder open to find a resistor. Every time I'd slow to idle or (gasp) use the headlights, my radio would die.

I think a previous aftermarket radio used a voltage dropping resistor, and the wiring was reused for the new aftermarket radio, thinking it was a fuse holder.

[PLP]

Interesting.
No, I have not checked yet. I have not noticed headlights making a difference, though. I will for sure check.
Thanks,