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?