my blower motor quit in r.v. tested it to be good. changed out the resistor still no power.?

Sure it could be the switch or fuse.

That is why you should start with a test light instead of just replacing things like a resister pack.

There is a stream of current flow, from the ignition switch, to the fuse block, to the fan switch, to the resistor pack, to the fan, and finally back to ground through the chassis, to the battery.

If everything is equally accessible, the fastest way is to divide the path in half by trying in the middle of the flow first, and then if good, move in the middle of what is down stream. If bad, then move in the middle of what is up stream. But when things are sometime hard to access, start with what is easiest.

And with an RV, don't assume any metal is well grounded to the battery negative. They use a lot of wood in an RV.

Check the ground wire sounds like it is not making a solid connection and yes resistors can go bad as well as the switch however you should still have twelve volts at the switch. See if have 12 volts if not then check the ground wire. Run a jumper ground wire or temporary ground wire to see if it changes and gives you power at the positive wire.

YEP! Buy a test light and start at the fuses!