I'm at a loss.

I have an older trolling motor on my little pontoon boat. It's 80 lbs and move the boat very well.

The problem is the foot controller. Most of the time it works great. It will be doing fine and then just stops. When you engage the ditch nothing happens....you can hear the switch, and a click in the head unit, but nothing else. If you switch from momentary to continuous, unit works fine. Stow it...move to a different place, it might or might not work properly. I suspect a short somewhere, but have zero idea how to fix it...

Look at the switch located in the foot pedal wire might be loose. Might also be the splice up in the head 3 screws should pop the top off. Look for melted wires in the head or bad splice connector. Not much to them get a meter out and test switch in foot pedal it might be wore out.

If it won't turn off, you have a short. If it fails to operate, you have an undesirable "open circuit". This could be a loose connection or a failing switch. When you switch to "continuous" you are simply bypassing the momentary push-button switch. You have stated it ALWAYS works if you switch to continuous. That makes me 99% confident your issue is very close to the momentary switch, or possibly even THE momentary switch.

Check that connections to the switch are tight. Check that the switch is correctly positioned so that pushing the button fully actuates the switch. If the plastic housing is cracked, the switch can move and you need a new one. Hold the switch down and wiggle wires to it. If it begins operating, you may have a wire broken inside insulation (not common). The most common is loose connection to switch, or bad switch. Easy to replace, just buy a new one and shotgun it!

Looks like I lied.

It had always worked before, but not anymore. Died yesterday and will not function in any mode. Batteries are charged up.

Reading Motorguide sites, this can be fixed by changing over to digital from the analog system. Cost is around $450 or so. Not sure it's wise to sink more money into a a twelve year old or older trolling motor.

I have a 109 lb thrust Motorguide that I have never installed. Thing is probably fourteen years old. Think I will put it on the bass boat and move the 60 lb thrust unit to the pontoon, take the savings to play the lottery in hopes of winning enough for one of those fancy remote controlled units.

Probably not a good plan, but it's my plan.