Jdaniels1730:
but this is on a transmission driven jet drive for a boat.
I'm not picturing what you're trying to do. Maybe when you send the drawing it will be clearer.
Allow me to paraphrase: you have two controllers and two solenoids. Currently you have an extra switch that reverses which controller controls which solenoid. But what do those controllers actually do? Are they forward+reverse controls or just on+off?
What is the voltage and current for each solenoid? AC or DC?
You have discovered that PWM won't work on mechanical relays and it may not work on SSR's either. (If the control current is AC then it's more difficult.)
Assuming PWM control works, I don't see how mixing the two controllers together will help. Let's say we have 25% duty cycle. So 75% of the signal comes from the 'other' controller. But what if they are both set to 'forward'? Then you get 100% forward.