Mr.Dylan,
There is  ceramic windings next to plug in on drivers side of heater.
This is the speed windings.
It is broke.
There are 4 terminals there.
the second one from the back is copper colored this is the ground.
Hook ground wire there, and put twelve volt to each other terminal.
This will tell you if it is working or maybe terminals corroded.
This is the best way to see what is broke.
Good Morning.

Fred