Gauges for a new engine

[TyroSailor]

As regular readers will know (and possibly have heard enough of by now...) I have a new Vetus M2.18 in my Centaur. It was supplied with only a basic instrument panel and I'd like to fit a tachometer and coolant-temperature gauge. There seem to be three options:
- fork out £200 or so on the proper Vetus instruments, and pay the engineer to fit them
- buy some generic instruments from a chandler for £120 and either pay the engineer or fit them myself
- buy secondhand instruments at a boat jumble (or use the old ones from the defunct MD2b) and fit them myself

Is it essential to have instruments from the same manufacturer as the engine? Are they hard to fit?

[Hillary]

Temperature gauge should be a simple case of replacing the warning light pressure switch with a T-Piece and screwing the warning light back in with a temperature sender in the other end. Or vetus may have a place where the sender goes with a blanking plug in it. Wiring it up is simple.

Tachometer might be more tricky. Some take a RPM feed off the alternator some use magnets others Opto electronics. i would see if you can find out how Vetus do it and then see if there are any compatible third party kits.