If you don't have a starter relay for the 12v/24v starter you're using, that's step one for a diesel. Starters are super straight forward, just need good gauge wire to the starter from battery, good ground and make sure the +12v switch feed is reading at the starter. If it isn't, work backwards.
Beauty of adding a starter relay is that you can use current 1hz starter relay, connect to the +12v feed from ignition and connect to constant +12v and ground. Super easy! You can really dig in and use
But also curious if the issue was resolved and what it was