I've done that on my PV (after the floor switch exploded in sparks and smoke, leaving me suddenly in the dark on a curvy country highway *shudder*) and it works perfectly. The wiring loom that reaches down to the switch also easily reaches into the engine compartment where I put the relay. The tuen signal pull-back switch is hooked to a gray wire that protrudes from the wiring loom on the left side about midway along the engine compartment - just forward of the heater assembly. Its a short unstripped stub of gray wire.

Get a 140 or 240 wiring diagram and study the wiring to the dimmer a bit - there's not a lot of wiring to do. I spent about 10 minutes staring at the wiring diagram (the relay terminals are all shown on the diagram), then about 25 minutes hooking wiring terminals on wires and plugging it all together.