89 starting problems

ive seen many posts with the same probs, truck sometimes starts sometimes not. had this problem forever it seems. i just replaced the motor, starter, altenator is fairly new, good battery new connections. a common cause ive seen in the forums is faulty wiring between the ign switch and starter. a common solution ive seen is to bypass with a push button. if this sounds right how do i go about doing that?

The short version -
You need a good quality Normally Open pushbutton switch
One side of the switch connects to a switched +12V source (switched meaning you have to place the Ign Sw in the RUN position to get the +12V)
The other side of the switch connects to starter
For safety use an inline fuse on the +12v side of the switch

To start the engine, place the Ign Sw in the RUN position and push the button to start.