I'll chime in. Correct me if I'm wrong.

I would check for power and control on the seat and steering wheel wires right at the connector.

With the circuit at fualt loaded (on) (let's just assume it's a power side switched design, and a two wire connector), connect test light to ground.

If the test light doesn't light, you may have an open.

Connect the test light to power.

If you touch the feed or control wire and the test light is lit, you have a short to ground on the wire or a TINY chance of a shorted driver.

If it's a three wire connector, the extra wire is a signal return (ground), if you have high voltage on the signal return your ground is bad or open.

Also another thing you could do is a bypass test, assuming your feed is good, if you connect the test to the control wires the seat or steering wheel should move.

I'm at work and I have to go now, I'll add more later.