This 4 position, fan switch will run your 3 speed heater fan without complicated relay wiring. 

Fits in 11mm hole. 1/4" Spade terminals.

63mm dia bezel, 23mm front projection, 35mm rear projection.

It also has a live out terminal for a warning light or compressor control system. 

Wiring Connections B-Live feed to switch, L-Speed 1, M-Speed 2, H-Speed 3, C-Live out in any on position (e.g on warning light)

Rated for 20 amps.

Note: Your motor must have windings for three speed operation.

3 SPEED FAN SWITCH #SWFAN6