Other than checking connectors and wiring leading into the left control switch to make sure they have good contact,cleaning the crevices of the switch with contact cleaner that's about all you can do with this switch. Some have been able to take them apart and cleaned any corrosion on the plates,but most end up with springs and brass plates flying out.Not uncommon for these switches to have to be replaced over time.Forgot to mention there is a 20 amp breaker in a plastic pouch that supplies power to the switches. If it's corroded or shorted out that can be the problem. Should be located close to the battery. Check for power on each side. If it doesn't have,slice the pouch open and replace it. Cheap part at most auto stores. Item #2 on the parts break down.
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Ok I will try that first. Once I get the machine running I can flip the on off switch to off and the quad shuts off but when the switch is in the middle the red light isn’t on. I’ll try that circuit breaker and see what that does.