Bought a 90 model champion and going to replace trolling motor. It has a 12/24 evinrude and want to replace with a 24 volt Minn Kota. Motor I have now is hooked up to 3 wires coming through deck. Can I wire straight 24 to these or maybe buy the plug that will fit the female plug at front of boat. Or will I need to run heavier wire to front and hook trolling batteries together? What is the best way to do this change?

You only need 2 wires make the 24 V jump at the batteries.  Check and make sure your wire is at least 8 gauge.

6ga wire is the norm nowadays

So even with the 12/24 plug in being at the front you would recommend running new wiring and connecting batteries together? I can do it but would be much easier to use plug if it is safe and not a fire hazard.

You should be able to use the existing wires if they are at least 8ga. You'll need a new plug/receptacle and a 60 amp marine circuit breaker or fuse near the batteries.

No you do not need to replace the receptable and you can use the same trolling motor plug.

 

Just use match the boat wires for your hookup at the receptacle with the trolling motor plug. You already have the jumper at your batteries.for 24V.

 

Technically you do not have to change the receptacle hookup at all. Just put the trolling motor cable on the 24V terminals of the plug.  You won't have a 12V connection on the plug anyway.

If you are getting rid of the 12/24, PM me, I'll compensate you for it!!