Larson, 4.3 GL-J, SX-A electrical gremlins

[Engident]

Hey guys
2008 Larson 180 Sport, 4.3 GL-J, SX-A outdrive. I am brand new to this boat, to the 4.3, and I/O in general. Brand new crate engine (long story, not my fault), new exhaust manifolds, new intake manifold, new Holley carb, outdrive input shaft seal replaced.
After the new motor was installed, these electrical gremlins appeared:
1) Trim gauge not working
2) Oil pressure gauge not working
3) Alarm (little red thing hanging under dash) going off continuously with ignition on, even after engine started.

I suspect 2 and 3 are related. Is this most likely the oil pressure sender? Is there more than one? Where is it located and how do I check it?

for trim gauge-- sensor looks aftermarket and new-ish, so may have been replaced shortly before I got the boat but was not replaced during the work I had done. I found what I think is the plug over the back of the motor-- 3 wires coming thru transom, 2 wires on end toward dash, it is firmly connected. Should I just go ahead and replace the trim sender, or is there more sophisticated testing I could do here to narrow down the issue?
Thanks guys
David

 

[alldodge]

I would look closer at the 10 pin harness connector. Numbers 2 and 3 are dealing with 2 different wires going thru the connector. The trim gauge has it's own separate wire and is powered by the purple wire at the helm

 

[muc]

or is there more sophisticated testing I could do here to narrow down the issue?

why yes there is!
trim gauge ---- disconnect wires back by transom. with the drive down, connect an ohm meter to the two wires that go to the sender. should read 10-12Ω. now use trim switch to raise drive while watching ohm meter, it should smoothly go up. if it passes, with the key on, jump the two wires that go to the dash, trim gauge needle should jump to the other side of the gauge.
guessing 2+3 are because someone miss wired replacement engine. oil pressure gauge is the dark blue wire, find it, disconnect it and touch it to ground. with key on gauge should jump just like trim gauge did.
tan with black tracer wire is for the warning horn, it should connect to 4 different senders, one on each exhaust manifold, one for water temp and one for oil pressure (if any of these wires touch ground the horn should sound). did tan/blk get switched with dark blue?

 

[Engident]

why yes there is!
trim gauge ---- disconnect wires back by transom. with the drive down, connect an ohm meter to the two wires that go to the sender. should read 10-12Ω. now use trim switch to raise drive while watching ohm meter, it should smoothly go up. if it passes, with the key on, jump the two wires that go to the dash, trim gauge needle should jump to the other side of the gauge.
guessing 2+3 are because someone miss wired replacement engine. oil pressure gauge is the dark blue wire, find it, disconnect it and touch it to ground. with key on gauge should jump just like trim gauge did.
tan with black tracer wire is for the warning horn, it should connect to 4 different senders, one on each exhaust manifold, one for water temp and one for oil pressure (if any of these wires touch ground the horn should sound). did tan/blk get switched with dark blue?

Thank you, I will check on that next opportunity.
Today's issue is that the "power steering reservoir" (if that's what Volvo calls it) passively drained itself sitting in the driveway. So I'm guessing there is a low-side leak. But my question there is: what is the consensus here about Volvo-branded fluid vs Dexron III?

 

[muc]

A little less of a chance for foaming with VP fluid. ATF is fine.

 

[Engident]

why yes there is!
trim gauge ---- disconnect wires back by transom. with the drive down, connect an ohm meter to the two wires that go to the sender. should read 10-12Ω. now use trim switch to raise drive while watching ohm meter, it should smoothly go up. if it passes, with the key on, jump the two wires that go to the dash, trim gauge needle should jump to the other side of the gauge.
guessing 2+3 are because someone miss wired replacement engine. oil pressure gauge is the dark blue wire, find it, disconnect it and touch it to ground. with key on gauge should jump just like trim gauge did.
tan with black tracer wire is for the warning horn, it should connect to 4 different senders, one on each exhaust manifold, one for water temp and one for oil pressure (if any of these wires touch ground the horn should sound). did tan/blk get switched with dark blue?

Ok bear with me here. So this is port side rear, above where the GM oil filter would be. The wire in the pic marked in green is definitely the alarm wire.

I checked the terminal on the sender circled in blue to ground... 1 ohm engine off/cold, about 1200 ohms engine running. Either way, running or not, the alarm sounds continuously until I unplug this wire. So my questions are:
1) are there separate senders for the alarm and the dash gauge? If so, where are they, respectively? (dash gauge isn't moving, stuck at mid scale at all times )
2) which sender is this in the pic.. alarm or gauge?
In other words,is it possible that the oil senders or their wires got reversed? Or is this switch wired correctly and it is just bad?
3) I was told there is another oil pressure sender somewhere behind the carb... I have not dug that far. If that's true, what is that particular sender for?

Also... What is this electrical thing over the actual oil filter?


Finally, can confirm neatly from your test, trim sender is definitely bad and trim gauge is good. Sender resistance only weakly and discontinuously correlated with trim angle, and it never went below 109 ohms. Thanks again!

 

[muc]

1+2 - this is the oil alarm sender, replace it, it tested bad.
3 - oil gauge sender will be aft of the carb, very near the distributor. Test it just like you tested trim sender. Dark blue wire.
That thing in the second pic is the fuel pump and that's the fuel filter under it.

 

[Horigan]

@Engident Alarms are generally driven by switches, with a single connector that provides open or ground to the alarm (oil press switch, water temp switch). There are separate oil pressure sensors and water temp sensors that drive the gauges. These typically have two connectors and provide a variable resistance.