One-off project, need sanity check

MCP3428 4-Channel 0-20V Analog to Digital Converter with IoT Interface

I’m working on an odd project with an old car, with a convoluted story that I would be happy to share if anyone is interested. The short version is I have worked out a logic gate solution to allow me to take the original wiring for the gear shift indicator (activating simple electromagnets to attract a needle) and re-route them to activate those electromagnets in a different order, compensating for the different gear shift pattern in a modern transmission. I set up the circuit on a breadboard to activate automotive relays using 12v automotive CMOS chips, and everything works as expected except for one minor detail.

Since the input voltage is selected via a rotary contact dial, there is constant current from one input state to the next. When testing using pushbuttons, pressing the proper buttons activates the proper relays, but when simulating the analog action of shifting gears (pressing one button, then continuing to hold it while pressing the next button in the sequence - this is necessary because the rotary dial never breaks contact when shifting from one position to the next)) the circuit does not recognize a change in inputs, just a second, additional command.

I need to introduce an interrupt somehow.

I thought about using the above ADC to change the incoming voltage to a refreshing digital signal, which seems like it ought to work. It’s a four channel device, and I need three inputs and three corresponding outputs. I’m using 12 volt automotive components to avoid having to step the voltage down, plus I’d rather have sturdy components when it will all be attached to the firewall, what with vibration, heat, cold, moisture, etc.

Does this sound like a workable plan? Will the MCP3428 work for this? Am I basically a complete novice fiddling around with something way over his head, but might have a viable solution for something no one else is ever going to need to do?

Any advice welcomed. Note that I left out most of the details of the circuit, which uses transistors to activate the relays, pull-down resistors, a few diodes, etc. That entire portion of the circuit seems to work perfectly, although I have a friend looking it over for efficiency, excessive heat generation, etc. The major issue I’m struggling with is a way to introduce a refreshing interrupt so that the gates will recognize the current input situation properly.