I am upgrading my son's HBX 1:18 truggy. I have purchased a 3 wire servo to replace original 5 wire servo. I need a diagram or some guidance. I have everything I need I believe, just lack knowlege.

That looks like proprietary hardware there. It is best if you replace it like for like. Or you'll have to replace the receiver and ESC to accommodate a 3 wire servo.
What's wrong with the original servo?

generally, it's easier to buy a 5 wire servo, but some have made their own conversions:
https://www.rcgroups.com/forums/show...ire-main-board