Trim Gauge Issue

Nitro2014

Seaman Apprentice
Joined
Jul 10, 2014
Messages
32
First, I must say thank you for everyone who took the time to help resolve a couple of boat issues I had within the last couple of weeks. It seems like things just keep coming up here recently. Oh, the joys of boat ownership! I would like to solve the issue with my trim gauge not working. I tested the voltage to the gauge and the results are: 3.27 v between G and S connections. 8.81 v between I and S. 12.06 between G and I. I tried testing the gauge by leaving just the ignition and ground wire connected and providing power. Gauge did not respond. I then shorted the sender wire to the ground on the gauge with the ignition and ground still connected and the gauge again did nothing. I then switched my tester over to Ohms, went to the outboard, traced the sending unit wires to the motor and tested the connections. The tester kept jumping all over the place and I couldn't get a conclusive ohms reading. I pushed the sending unit in manually while testing and did get a little response, but again nothing conclusive on the number of ohms. All connections were cleaned and tightened. Prior to the gauge not working entirely, it was flickering when raises and lowering the trim. Is it possible my gauge and sending unit went out at the same time or am I doing something wrong with my testing procedures? Thanks!
 
Joined
Oct 22, 2007
Messages
2,598
or am I doing something wrong with my testing procedures?


That.

Trim senders are nothing more than a variable resistor. Different manufacturers use different resistance values for full up and full down, but they all should show a smoothly varying resistance as the sender moves. To test the gauge you'd have to hook up an appropriate potentiometer to simulate the sender.

I don't have the resistance values memorized for the various manufacturers, but you should be able to find that online easy enough with a little searching.
 

jhebert

Ensign
Joined
Jul 24, 2005
Messages
902
I have never seen a New York Times editorial on trim gauges, so I don't think there are any issues about them.

In your case, you have a minor electrical problem of the simplest kind. The trim indicator is a simple circuit in which a meter is connected to reflect the resistance of the trim sender. There are only a few elements in this circuit:

--a source of 12-Volt current positive polarity

--a meter, inserted in the current path in some manner, not quite known,

--a variable resistance sensor linked mechanically to the engine trim position

--a return path the the current source's negative polarity

The current flows from the source, through the meter, through the sender, and returns to the source.

The trim meter is not exactly a completely simple little circuit. It is often actually a bridge circuit, with the sender being connected as one part of the bridge. Connect the 12-Volt (+) to the I terminal. Usually if you connect a resistor from the S terminal of the meter to the current source negative return, the meter will move to some indicated value. Try a 100-Ohm resistor for starters, as that ought to be in the resistance range of just about any trim sensor. The meter pointer should move. If it does, the meter is good.

Your narrative of your resistance measurement process sounds like the sender is defective. The resistance should not "jump around." It should be steady at any fixed position of the trim sender, and change smoothly as the trim position moves.

Check all the intermediate wiring and connections. There may be problems in that part of the circuit. If the wiring to the sender moves as the engine moves, it may be a source of problems. A lot of flexing may have broken a conductor.
 

Nitro2014

Seaman Apprentice
Joined
Jul 10, 2014
Messages
32
Thanks for the information! Just to clarify, based on the information I provided, will installing a new trim sending unit solve the issue? I would be happy to check or answer questions if I need to in order to solve the problem with just one replacement. I would rather spend several hours gathering thoughts and running tests than to spend $$$$ replacing part/s that were not the issue!
 
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