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Brake switch, line lock and trans brake wiring
FT600 and Hardwire PDM.
I have wired the components per Fueltech's wiring diagram for brake switch, line lock, and transbrake. Is it best to wire an output from Fueltech to a Input on the Hardwire PDM to control all the functions? Any other suggestions on wiring is appreciated.

IDK if you can get the PWM duty thru can, but if you can, instead of using a SSR, use an output driven by the PWM duty readed in the can bus.
If not, maybe you can figure out how read the PWM duty with an input in the PDM, and drive the output with that value.