Plc component advice

Hi all just a quick question I'm looking for advice to add on to an existing relay logic system. Basically I want to tie into a relay logic control panel that has 40 connection points and then runs to a group of solenoids and a rpm pick up. I would like to eliminate the 40 wire cable and have just a power,common, and communication. If any one has some input on this it would be great. Also it's a 24v setup. The reviving unit needs to be quite durable due to vibration and possible elemental exposure. Thanks again I know it's a tall order but any input it appriciated.

The revised unit needs to be quite durable due to vibration and possible elemental exposure.

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Then what is wrong with the old relay control panel? You already have the 40-wire cable installed and paid for, so why replace that with a communications cable that only works if your devices on each end are able to send and receive messages in spite of vibration, rain, sleet, whatever?

The problem with it is that the cable needs to be replaced often so from a financial standpoint it's more economical in the long run.

You could replace the relay panel with a new watertight box with a PLC inside, and mount it on shock absorbers.