I have the engine of a 82 yamaha maxim 400 that I want to put on a gocart but I can't figure out how to put the wire harness together.Can someone help me?

I would start with the Shop Manual for thr 82' Maxim(With Schematic)
Most important wiring needed will be Ignition and Starting Circuit, Charging Circuit, plus any light, horns, signals you want to add.
Tail/Brake lights.
Watch for any kill(interrupt) circuits(like Neutral Safetty, Clutch switch and Throttle kill switch.

Here's your Service Manual, Wiring diagram is on page 244:
http://www.files.pioneerx.co.uk/view.php?f...vice_manual.zip
This diagram is perfect for your application, you could white out the items not needed(turn signals, etc.)

I just went on my link I provided above, but is now gone, hope you got a copy already?
I eliminated everything after the UK, and got this:
http://www.files.pioneerx.co.uk/index.php?dir=Motorbike%20Files