Here are a few relays. I'm only using the 15A and 30A but Mercedes does make more. I can't remember which one I ordered and which one I picked up at a junkyard, but all are still available from the dealer (can't remember the price but it wasn't much).
These are just like the ice cube relays EXCEPT that the fuse is external to the case and replaceable.
Part numbers:
15A -- 002 542 01 19
30A -- 001 542 96 19
40A -- 001 542 97 18
I will be putting in a 10A fuse in the 15A relay and a 20A Fuse in the 30A Relay.
These are the coolant temp sensors that I'll be using. I'm not sure the location of each yet but that'll come soon.
Part numbers will vary as these are used on plenty of marques including Volvo, BMW, etc. But I know these will fit the threads of the coolant ports on the OM603.
FAE:
87/82 °C -- 36050
95/90 °C -- 36010
