Is It The Gauge Or Sender???? Arrrrh!!!

[paultallett]

On our way to Cowes yesterday I started to get irratic readings from my leg trim gauge!! (Mercruiser Mag 350, Bravo 3 leg & Faria trim gauge) It used to be rock steady and move in perfect sync with the leg. On Sunday as I would trim up from the '0' postion the gauge would show that I was triming down.....then suddenly shoot to a '+' reading......then flicker about a little until it settled in a completely different reading......and so the game continued!!!!

Once at Cowes, I checked the the leg was doing as it supposed to, I cleaned the wire conntacts coming from the transom plate along with all the contacts at the back of the gauge but it has made no difference!!!

Does that sound like a gauge fault or is it the sender unit on the leg?? I can replace the gauge easy enough but can't get at the sender unit with the boat in the water.............Don't know where to start.... /forums/images/graemlins/blush.gif

Regards,

Paul.

 

[Elessar]

Almost certainly the sender - a mercruiser weak spot.
The cables go porus and water creeps into the sender unit.
It isn't the end of the world so wait till you next have a lift out. It will just get steadily worse but the guage isn't essential.
They look simple to replace but to feed the cable through you have to remove the leg and gimble, so do it at the same time as your bellows.
Replace the trim limit switch at the same time, in fact when you buy them they come as a pair (the guage sender is on the sbd side of the leg, the trim limit switch looks identical and is on the port side)

 

[ExcaliburII]

Agreed - almost certainly the sender. May be worth opening up the sender unit and cleaning up the track if the cable is not obviously broken or cracked. Make a mark on the sender and leg, and note the position of the spindle in the sender as you take it apart, then it will need minimal or no adjustment when you refit it.

You can actually rewire these if the problem is with the cable. I replaced my cables with some heavier gauge extra-flexible stuff I had lying around as both sides had failed but the sender and switch were OK.

Still need the boat out of the water to do any of this and the leg off to replace the cables, though. /forums/images/graemlins/frown.gif /forums/images/graemlins/frown.gif

 

[paultallett]

Thanks guys......I feared it wouldn't be as easy as replacing just the gauge!! I got in to the hang of guessing the leg trim on the way back from Cowes.......Any tips on working out my leg trim with guess work?? I was watching my wake and the attitude of the bow, any more ideas??

 

[ExcaliburII]

If you watch the leg whilst moored and note the time it takes to get from fully down to level (ie what would be parallel to the surface with the boat in running trim) you just need to trim up for this amount of time after starting off. Then fine adjust from there, based on conditions etc.

This assumes that you trim fully in before accelerating on to the plane, of course. Oh, and time it with the engine running, as the hydraulics will work faster when the battery is charging.

 

[paultallett]

Thats just what I was thinking.....

You say you rewired them? I've just spoken to my Mercruiser dealer and he told me what a pain they are and if I can live without, do so cause they take around 3 hours labour to change, due to threading the wires back in the transom. How did you find the job yourself??

 

[lovezoo]

I would certainly test the gauge first, before going to the trouble of replacing the sender, as gauges do fail. You can test it by disconnecting the "S" connection on the back of the gauge. Now turn the ignition on - the gauge should show full deflection one way. Now connect the S on the gauge to ground and you should get full deflection the other way. If it is not doing that, or it is sticking, you have a problem with the gauge.

Got to be easier to check that first before replacing the sender.

 

[paultallett]

Thanks for that. Sorry to sound really stupid, when you say 's' connection, which one would that be? The back of the gauge has 3 pins, on to which fits a semi circular plug. 1 is +, 1 -, and the other from the sender??

 

[lovezoo]

On mine, it just has studs to fit ring type connectors. The three connetions are +ve, Ground and Sender. You may also have a connection for lights. They will work the same way, irrespective of the type of connector. If you have a multimeter you should be able to work out which connection is which on the plug using the volt range - you could also test that the sender is working that way.

On mine I had an intermittent fault, with the gauge not working - and it was just the gauge that was faulty.

 

[ExcaliburII]

Wasn't really too much hassle to rewire mine as, when I bought Excalibur II, the steering arm was loose on the top shaft in the gimbal ring. Everything had to come off to fit a new arm and top shaft, and I could see the wires were a bit iffy when I stripped it all down. It's a long time ago now, so I can't remember the detail but I cut the standard wires back and connected them to a junction block fixed to the transom (inside, obviously /forums/images/graemlins/grin.gif).

Then took the sender and trim switch to bits, connected a length of new twin core extra-flex to each, reassembled and tested them with a multimeter, then poked the ends through the existing gland in the transom plate and ran them to the junction block. I honestly can't remember now whether they were solder connections, crimp terminals or whatever in the senders.

This was a very minor part of the whole rectification process - the whole unit was so manky I stripped all the parts back to bare metal to prime and paint everything before reassembly.

The trim sender and limit switch have been working perfectly now for 8 years *touches wood*, hence my assertion that it is possible to rewire them. In the event of any problems, the junction block on the transom is easily accessible with a multimeter to aid fault finding, but has not yet been needed. Bit like carrying an umbrella to ward off rain I suppose: if I had done an inline connection and insulated and sealed everything no doubt I would have needed to break it all down several times by now. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif