Atwood RV Furnace will not start after changing propane cyl

The 'timed delay relay' is part of your ignition control board.

Some models it is a stand alone relay......power from ON/OFF switch/CB went to the relay and then to blower motor AFTER power come from T-stat that energized a coil which when heated made up path in relay for power to blower motor.

You have power to board and power from T-stat....blower runs when you jumper power.

Bad ignition control board OR bad connections/ground on board.

Replacement board......Dinosaur Board LINK

Atwood 8500 Series Manual (Limited but has wiring & part numbers) LINK

Atwood 79/80, 85 & 89 Series Manual....more info with troubleshooting LINK