Hi Rik
Never figured that one out since i didn't find time to search it out - but best bet is to get the diagrams for a w201 Cosworth 190e, since they had an oil temp sensor from factory and see where that one fits....either oil sump or oil filter is likely placing.
Then just use the Cosworth sensor piece but hooked upto the wires on the Brab kit.
talbir
Ps yes, Jay is new owner of that silver 500E i owned....most stupid thing i did in my life was sell that car. Gorgeous piece and irreplaceable for me. But i have got a another 500e recently...a Spruce Green one...with lots of Brab bits again....