MD1B no oil pressure light when key is switched on

"Got a 1974 volvo penta MD1B,

"Got a 1974 volvo penta MD1B, and the "warning lamp for oil pressure" red light on the instrument panel has stopped lighting in the pre-combustion when i turn the key switch. it worked correctly (on when key is switched, then off when engine starts), then i did an 8 hour run of the engine, now when i turn the key switch the oil pressure warning light doesn't come on. i periodically checked it during the voyage and the light never came on, and engine worked well. got a little black oil in the bilge (this engine is new to me, so not sure how much is normal), but oil level is ok (though oil is a season old). there is no oil pressure gauge. i haven't tried to restart the engine.

after changing the oil/filter, and cleaning the strainer, i assume the first thing to check is the bulb itself.... and after that? oil pressure sensor? where is that sensor -- i can't find it in the workshop manual - - and how would i test it?

i'm pretty much a novice so any help appreciated. thanks."

"Switch is right next to oil f

"Switch is right next to oil filter. Has single wire attached. Unhook wire with key on and ground wire to block. Light on panel should come on. If so, switch is bad. If not, bulb may be bad."

"Thanks yeah that was it. ove

"Thanks yeah that was it. overtightening the wire screw, or overtightening the whole unit, causes an internal break in the ceramic that will leak oil at a steady rate when engine is running. $40 later...."