Sending unit questions
 

I'm setting up my new engines and can't figure out what these sending units do. I thought I did but met with a guy at shop where I was going to buy new sending units (to operate the alarms at the dashboard) and he didn't know what I needed. I have attached a few pics. FYI, these were on my stock 7.4's and as far as I know all factory installed.
There were 2 units in the thermostat housing. I pulled them out and they are different. 2nd pic. Does one of these operate the alarm at the dashboard? I ask this because there was also another unit (the largest one pic #3) installed in the block by the starter. It's actually in the "block drain location" I thought this was maybe an overheating sending unit but maybe it's for water pressure? That sending unit also is the only one that had a GM clip for the wire instead of the sending unit having a stud and the wire held in place with a washer and nut. The last fitting was mounted in the block above the oil filter location. I think this is for low or no oil pressure? Thanks for your help.
https://cimg7.ibsrv.net/gimg/www.off...6e4edc9555.jpg
https://cimg9.ibsrv.net/gimg/www.off...3056bb9941.jpg
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The knock sensor is the one in the block drain.

The 2 in the thermo housing, one is for the gauge, the other is probably the alarm buzzer.

One above the oil filter adapter is for pressure but I am unsure if what you have there is for gauge or buzzer.

Did they install knock sensors in 1995 on a 7.4 that is carbureted?

If its got the Tbolt V ign module then yes it can have a knock sensor...

or maybe you have a motor that was in that gray zone when they were transitioning over to EFI and were still using old stuff to get rid of things :)

Well I ditched whatever was there for the MSD ready to run stuff. Just out of curiosity this is what was there. Did this use the knock sensor? Mercury is a big outfit and it could be that it's cheaper not to "think" about each engine separately and just wire them all the same. Shotgun affect. Can't go wrong with that.:D
https://cimg0.ibsrv.net/gimg/www.off...658805456b.jpg

I'm going with alarm. The one for operating my gauge is up on top kinda behind the distributor.

yes thats a knock module mounted to the distributor

if its in the block by the bell housing that an oil pressure gauge,

Oil pressure switch vs gauge sender can both work correctly in either location (top of bellhousing, or above filter adapter). It's oil temp senders that don't work well in low-flow or blind-ended passage locations. Good pressure readings available in either place.