Sorry, I believe model is CMP50SL with GM V6 engine, don't have serial yet, about 3-4 years? old, light doesn't come on when first started, comes on after started about 1-2 minutes, oil and temp lights work and fluids ok, don't know what connector to plug a handset into if can be done either, possible check engine light? starts and runs fine

It "could" be the engine low oil pressure/high coolant temperature warning light.
But as powerlifter stated provide what model Clark & serial number are you talking about to get a more accurate answer.

Does it have a woodward fuel system? Give more info and email address.

Maybe if you told us what the Model and year of truck was someone might have the answer