Oil Pressure Gauge Pegged

[MD106]

Hi All,
I'm looking for some assistance as my starboard oil pressure gauge is below 0 with engine off and pegs to the left when in start or running position. We have an S42 This is a piece of mind item as we had engine overhauled and the gauge doesn't work as it did before.
Replaced 3 wire sensor with no improvement.
Mercruiser has 805267T as the sender but I have no idea where that is on the block. Looks like a single wire unit. Any thoughts, possibly a short in a wire.... Thanks Mitch

 

[gordmac]

When you say let's to the left do you mean it reads maximum value? What do you mean by sensor and sender?

 

[MD106]

Hi, the gauge is reading below its minimum value for pressure, when I turn ignition to run it moves the needle on the gauge from 0 to well below 0.
I've attached photos of the sensor first pic and sender 2nd pic.
Thanks
Mitch

 

[gordmac]

What does each one do and which is connected to the guage? Has only one been changed and did that coincide with the problem?
I think the guage will operate with a resistance that varies with pressure, some go up with pressure others down. If the guage is going the wrong way it could be because the sender goes the wrong way.

 

[gordmac]

I suspect the sender in your second pic operates the guage, what happens if you take the wire off? Then if you earth it?

 

[William_H]

My guess is that the guage has been connected wrong way around causing needle to move backwards. If I read OP correctly. ol'will

 

[KevinV]

For a single pole sender the gauge is a simple ampmeter. It has a (ignition) switched live in, and a live to the (variable resistance) sender out - using the block as ground. As ol'will says, if the live in an out are switched on the gauge it'll read a negative current, so work backwards.

Easy to check by disconnecting one or the other and seeing which is live (with the ignition on). Take care with the loose wire - there's a 50% chance it's live.