Which engine do you have?? Is it the MD11D or the MD2B, either way it doesnt really matter.
Both these unit have the optoin of a temp gauge and sender from Volvo Penta, the sender is located in the top of the exhaust manifold, and powered through the engine wiring loom.
Both engine use the same kit. (VP RRP + Vat)
841233 gauge £88.67
840074 sensor £21.99
957181 seal for sensor £0.46
No doubt someone here will have a source for cheaper kit from some aftermarket supplier!!!
Yes there is a way, I've done this very succesfully and easily with a £7 unit from Halfords. Can't quite remember the details of how I did it, but will have a look this weekend - ring me on 07814 942533 and I can give you chapter & verse.