Trim tab operation knocks Garmin GPS funtion offline

The wireway to the Garmin 4212 on the bridge is tightly packed.
Thinking however, that I may need to run dedicated power and ground to the Garmin.
Is there a noise filter that might suffice?

Somewhere they have common power points both positive and negative that is causing a dip in voltage to the Garmin or active antenna. Try temporarily running a separate power lead from the battery to the Garmin and the problem should go away. I usually find the negative gets connected to a daisy-chained spiderweb of 16 ga black wires in the instrument cluster causing all sorts of problems. Good enough for gauge backlight, but not good enough to run a sensitive piece of electronic gear.
If that doesnt work then noise is coming from the trim tab motor.

I agree. Lots of equipment like this will not put up with voltage dips below a certain point. Usually caused by wiring that has become too small because more equipment has been added to what was, at one time, adequate for the then loads.
OR dirty, loose, corroded connections.

As High Wire suggested run a separate cable to the T tabs. Doesn't need to be pretty or neat, just run it as a test. Fuse it though as you don't need another problem.

If that stops the nonesense then look at what you can do. You may only need to redo the T.tabs with its own supply instead of from the back of the control panel.

You might also hook a DMM to the GPS power leads and operate the T. tabs and see that the v level drops to as a double check..

A filter will not help with a V dip from inadequate wiring.

Thank you guys. High Wire and C Lectric?
Sounds like I called up the big guns!

Just got back from KS in winter storage and indeed, confirmed shared positive and ground busses.
Will try to get a dedcated line up to the Garmin, as Tabs are dual control bridge and salon helms. So I think this might be the best solution?
Further thoughts welcome please.

Bennett Trim Tabs pull 18 amps, serious draw. The Garmin doesn't need squat, but as you know is sensitive. Can you find something else to draw power from to share for the Garmin? Instrument lights, accessory power, compass light, etc.
If you run a new line, run it for the Garmin, easier to run a lower power pair than for an 18amp load.

Thanks Keys. Yes, I will run a new line to the Garmin. I was surprised to find that Garmin states 3 amps max draw on this 4212. The screen and innards generate a fair amount of heat, plus transducer and external network 'box'..
I thought it would be more in the 6-10 amp range. So fusing should be 4 amps?

I would have thought that the Bennet was operating through solenoids with low amps to the switches. I will look at the switch supply lines too. Even for intermittent use, they may need upsizing.