How to wire a center channel speaker?

[Nodnarb76]

I have an 87 R20 Suburban that I am going to re-do the sound system in.
I have four speakers now and was wondering what would be involved in using four speakers in the stock locations and then put a speaker in the center and use as a center channel. Years ago on another truck I had a stereo shop did one for me by somehow wiring it with the front speakers, but that was 20 years ago and don't remember how they did it or if it would create any problems somewhere else.