Originally Posted by Wicked CAS

You might want to buy some of your parts from the installer... Specialy the wiring... make sure it is good brand and make sure it has good quality parts in there...

Reasons:
Well you will be giving him some parts business.
If anything goes wrong with that wire he should warranty it for you and labor would be observed by him.
If you bring him the wire and something goes wrong or it is defective, lets say an rca cable goes bad. He has the upper hand to charge you the labor for replacing that wire.

Same with the steering wheel module. Buy it from him and have him install it... He will also feel a little better about doing the install since you are atleast buying some parts from him.