Ventilation fan has stopped

[moltuae]

You could also diagnose it with a volt meter. If you put the meter across the motor first, that'll rule in/out a motor problem. Running normally, I'd expect to see a voltage that changes with fan speed. When the fault occurs (ie fan not running when it should be), 12 volts would suggest a motor fault and 0 volts a controller/power fault.

If the first test suggest a controller/power fault, attach the meter's ground to a permanent ground connection (leaving the positive wire on the motor's supply connection). Running normally, you should have 12 volts. When the fault occurs if you still have 12 volts the problem is with the 'hedgehog' (or associated connections), if you have 0 volts, the fault it with the supply.

[HPsauce]

Thanks Mark, I like the logic, but it means hacking into cables or connectors to get readings and it's all weatherproof connectors in that area, so I'll try the "plug and play" option first.

I'm guessing that the thin wires running off the thick power feeds near the beige connector are probably to measure the voltages as part of the HVAC control system and the extra yellow/red wire is a control signal to the "hedgehog". I would presume it's fins are purely for cooling what is effectively a variable resistive load.

[moltuae]

That would be my guess too. The yellow/red is definitely a control wire. If the controller is a simple high-power bipolar transistor, you'll probably see a voltage on that wire that varies with fan speed (probably 0-5 volts). There does appear to be some feedback/sensing connections too which may account for the remaining thin wires.

[moltuae]

Originally Posted by HPsauce

but it means hacking into cables or connectors to get readings and it's all weatherproof connectors in that area, so I'll try the "plug and play" option first.

That's where the 'bed-of-nails' croc clips come in handy