Help Sorting Out a Trim Gauge Problem Please

[Twolane]

Need help if anyone can. Boat is a late 70s Mercruiser 165 equipped Glastron. It had the trim sending unit and trim limit switch both fried. Their pigtails gone at the transom.

Inside the boat found the wire pair that goes to the trim limit switch. They're seen in one of the pictures. No certainty on the pair for the trim sending unit though.

In the rear of the boat coming back with the main harness I found the pair of wires that can be seen in what appear to be two shades of blue. They'd been cut off at the point you now see them stripped back a bit. I was hoping they went to the trim sender connections for no other reason than they were the only unused pair in the back of the boat.

The other picture shows the back of the trim gauge. Using an ohm meter both of the wires from that wire pair in question show continuity to every post on the back of the trim gauge. I then unhooked the lighter purple/violet/pink/whatever-color-it-is wire from the pictured bottom left of the trim and checked for continuity again. Once again both wires at the rear of the boat showed continuity to everything. Both to the now disconnected wire and to the ground and other post on the back of the trim gauge.

Not sure what I expected. But that wasn't it.

First off can anyone confirm that this pair in the back should go to the trim sender. I have two different schematics in hand now and neither are complete for that connection.

If that is or isn't the pair does the continuity to and through the gauge sound right. I was trying to think of it like a gas gauge and it's not behaving that way. Even wondering now if the gauge failed sometime and someone couldn't sort it out so just cut off the sender pair as a way to give up.

I realize the wire pair in the back doesn't color match the contacts on the back of the trim gauge. I can't find a splice along the harness's run up the right side of the boat. Perhaps it's changing colors at the connectors under the dash. This I can't say right now.

With the information at hand if anyone can offer an insight it'd be appreciated. Doing this so far with the battery unhooked. I do have another trim gauge here that could be swapped in if the descriptions make the currently installed piece sound defective. Also don't mind running another wire pair back to the sending unit's connectors if I knew for sure what/where they'd connect to.

Thanks.

 

[Jlawsen]

Re: Help Sorting Out a Trim Gauge Problem Please

The purple wires are for the light in the gauge. The red is the 12v positive, the black is the 12v negative and that other terminal in the upper right of your pic is where the trim gauge is supposed to hook up. It should be a a single wire for that gauge and should be black with a tan stripe.

It was probably hooked up and operational when the boat was new but if you didn't disconnect it, someone else did. It may still be laying in the area where the gauge is located or it may have been cut back. At this point, I'd replace the gauge and replace the trim sender and then re-wire it up to the gauge. It's just one wire and isn't that hard. 18ga wire is sufficient. Black and tan wire is hard to find so just use black and label it on both ends and at a any readily accessible points along the way. This will lessen the odds of someone tapping into it for battery 12v negative in the future.

 

[Twolane]

Re: Help Sorting Out a Trim Gauge Problem Please

Didn't find anything disconnected or cut back. So whomever beat me to it cut it back very closely within the larger harness. Will look again.

Just to circle the wagons and make sure I understand. The center posts are the ground. It daisy chains from there to ground the other instruments also. The purple wires on the bottom right (as pictured) are for instrument lights. That connection daisy chaings to other instruments as well.

The red wire as pictured bottom left is power to the instrument. With the battery back in I'll check it for power with the switch on.

The push on spade connector is connection for the sending unit? Does it matter which side? If a typical resistance type sending unit I assume not. But it's easier to be ignorant before the fact rather than after a mistaken installation. The trim sender has both a male and a female bullet connector. If a typical resistance type sending unit than the other side goes to ground?

If all that's so I can run one lead from the push on spade connector to the sending unit at the rear and ground the other side of the sender? Then, voila, functional trim gauge again.

Any idea what that unused pair of wires at the back of the boat are? Look like darker and lighter blue.

 

[Twolane]

Re: Help Sorting Out a Trim Gauge Problem Please

Got back in to this gauge problem this evening and got it sorted. In case anyone else as novice as I am should see it later want to circle the wagons and get all the info correct.

First off I couldn't find the wire from the trim sending unit to the trim gauge because the boat didn't have one (not just the wire, the gauge). It had a dummy fake gauge in the hole. Not knowing what I was looking at the dummy front fooled me. Boat never came with it. Apparently sometime in its life someone had installed a sending unit while also changing a trim limit switch not realizing the other wasn't needed. Since I found the obviously bad sender I just assumed the rest of the kit was in the boat and was fooled by the false front.

That pic from the rear was (obviously) not the trim gauge. It was just above the trim gauge location and was the fuel gauge. Wired correctly too. The purple wires are positive and marked on the gauge as I (ignition ?). The red gauge isn't a power wire. It's the leg from the fuel sender. That spade up top is not a sender feed. It is actually power to the gauges's light. It was obvious once the gauge was out in my hand and could see it closer.

The new trim gauge going in (in the now cut out hole behind where the false front used to be) is marked the same. Post marked I is the power. Post marked S for feed from the sending unit (with a new brown wire run from front to back). Spade up top for the light and the center post for ground. Not an unusual convention at all and similar to automotive aftermarket product for years and years.

It's all back in now. Even the gauge's light is hooked up as are the lights in all the other gauges. Only half of them ever seemed to have their light sockets powered. All works. All good. One more small task done.