Mercruiser 305 sensor/sender Questions

[evilpsych]

Just bought a basketcase 1986 build Mercruiser 230 (GM 305 w/ 4bbl Rochester Quadrajet) in my 1987 Sport-Craft Sportsman 230 (Hull #4375). It's one of the few INBOARD setups Sport-Craft made according to my research. Previous owner did a ton of 'modifications' that are highly suspect and his electrical technique leaves a lot to be desired (hacked wire that's taped back,wires run under carpet, bypassed stuff that I've almost all replaced/ripped out, and tested as good.

Engine Water Temp and Oil Pressure sending units/gauges are not working. I'd like to replace the whole batch - got a gauge set on order but I have multiple questions about sensor/sender locations.

I have a White with blue stripe wire running from a sensor on the circulating pump, to a sensor on the lower back of the motor (left side, low on the engine below exhaust manifold) then to a THIRD sensor on the gearbox/inboard transmission. then it goes to ground. Assume these are all water temps but why three locations?

There's an oil pressure Switch? Right next to the Distributor, but i can't find the pressure sensor itself?

There's an unidentified sensor in the intake manifold that doesnt show up on the exploded diagrams online.

Any help you can provide would be awesome to this

 

[Scott Danforth]

wiring colors are standard. just google SAE standard wiring. generally the oil pressure sender is next to the dizzy. only other place it could be is above the oil filter boss.

 

[alldodge]

Just bought a basketcase 1986 build Mercruiser 230 (GM 305 w/ 4bbl Rochester Quadrajet) in my 1987 Sport-Craft Sportsman 230 (Hull #4375). It's one of the few INBOARD setups Sport-Craft made according to my research. Previous owner did a ton of 'modifications' that are highly suspect and his electrical technique leaves a lot to be desired (hacked wire that's taped back,wires run under carpet, bypassed stuff that I've almost all replaced/ripped out, and tested as good.

Engine Water Temp and Oil Pressure sending units/gauges are not working. I'd like to replace the whole batch - got a gauge set on order but I have multiple questions about sensor/sender locations.

Water temp is color is Tan and Oil pressure is Light Blue

I have a White with blue stripe wire running from a sensor on the circulating pump, to a sensor on the lower back of the motor (left side, low on the engine below exhaust manifold) then to a THIRD sensor on the gearbox/inboard transmission. then it goes to ground. Assume these are all water temps but why three locations?

Don't know about a white/Blue but there is a Light Blue/white that goes to the trim up circuit

There's an oil pressure Switch? Right next to the Distributor, but i can't find the pressure sensor itself?

The one next to the distributor in most cases is the oil pressure sensor, but if it is a switch, then it would go to a light because you should not have an electric fuel pump.

There's an unidentified sensor in the intake manifold that doesnt show up on the exploded diagrams online.

Post a pic

 

[evilpsych]

Yeah Ive seen that chart. They don't match up at all. I think sportcraft had their own harness for the gauge cluster as opposed to the mercruiser one. This boat has Bennett trimmtabs also with the four color harness.

 

[evilpsych]

Which doesn't explain why what seems to be a water temp sensor is daisychained

 

[alldodge]

If its a temp switch it could be chained to the oil switch which then goes to the negative side of the alarm