Merc 7.4l Oil pressure switches

[thormx11]

I am in the process of replacing a mark IV 7.4l with a gen VI (used, from 2000 truck) and I want to replace these two oil pressure sensors. I believe one is for the alarm and one is for the gauge? On the mark IV, these were both directly above the oil filter. The gen VI only has a plug for one sensor by the oil filter and the oil pressure sensor was up top right behind the distributor on the port side. The pressure switch looked to be the same as the sensors on the newer style 5.3 GM engines. Is there any reason why I cannot use the newer style automotive sensor if I replace the single wire pigtail? Also, which of these sensors is for the alarm and the gauge?

 

[Bt Doctur]

pic 2 looks like the oil pressure alarm switch. It closes when there is no oil pressure and trips a buzzer or horn.
Pic 6 is the oil pressure sender for the oil pressure gauge.

 

[Scott Danforth]

Marine and auto usually use different resistance values

 

[achris]

.... Is there any reason why I cannot use the newer style automotive sensor if I replace the single wire pigtail? ..

Certainly is. An automotive sender isn't SAE-J1171 rated. (That's the rating for electrical equipement used on a marine engine. It basically certifies that the part will not initiate a fire or explosion).

 

[Bt Doctur]

And directions, knew a guy who replaced his with a auto part and it read backwards

 

[thormx11]

I will be sticking with my original sensors for now then. I will replace them with their proper replacements if needed since I know which is which now. I am planning to put the oil pressure sender by the oil filter and put the oil pressure alarm switch up top where the original pressure switch was. I will have to reduce it down a size to thread into the block.

 

[tank1949]

I am in the process of replacing a mark IV 7.4l with a gen VI (used, from 2000 truck) and I want to replace these two oil pressure sensors. I believe one is for the alarm and one is for the gauge? On the mark IV, these were both directly above the oil filter. The gen VI only has a plug for one sensor by the oil filter and the oil pressure sensor was up top right behind the distributor on the port side. The pressure switch looked to be the same as the sensors on the newer style 5.3 GM engines. Is there any reason why I cannot use the newer style automotive sensor if I replace the single wire pigtail? Also, which of these sensors is for the alarm and the gauge?

There maybe and most likely be an impedance issue with any sender/gauge. With switches, not so much. My boat's former owner disconnected oil pressure and temperature switches and only left senders. DUMB! Who wouldn't want an alarm screaming at them if something went bad or was about to go bad?