Today I installed the raw water alarm.  I purchased this unit, which has a temp sensor which straps onto the exhaust hose after the water injector.  If it gets too hot, it closes and completes a circuit to ground, just like the engine oil and temp alarms.  The idea is to warn me of the loss of cooling water before the uncooled engine exhaust cooks the exhaust hose and/or muffler.  This happened to me on a charter boat in the BVIs in January.  Black smoke billowing out of the engine room is no fun!

http://www.borelmfg.com/products_alarm.htm

There was room in my engine panel to install this, and it is shallow enough that it fit even in the center where the pod is shallowest to fit around the pedestal.  Hopefully the pictures below come through:

Cut  a 1-7/8″ hole in the panel

From the back, wired the + to the power terminal