Upper gauges not working

My flybridge oil pressure and temp gauges stopped working, tach and amp are fine. Checked the lower helm and all is good there. I am gauge challenged but I think that the senders go to the lower helm and then are daisy-chained up to the FB rather than separate senders on my 1987 FL SP135's. Any known suspect issues I should look for? My plan is to crawl back under the FB dash (always fun in Florida at this time of the year) and try to follow the wires to see what I find. With both oil pressure and temp going at once, there has to be some common factor or connection but I have no experience with how they are wired. Any comments appreciated!

Both oil pressure and water temp gauges will have a common source of 12v power to activate them. My guess is a poor connection someplace. You'll need someone to watch the two gauges after you have turned on the ignition switch to see if they start working while you check connections under the dash at all points where 12v power should be. Generally 12v power comes from ignition switch and is "daisy chained" from each guage to the next. Many boats use sensors that are designed for two gauges to work from. Don't know if GB's does that or individual sensors for each gauge.

Thanks, Bill. At some point, I will remember "simple things first". I would think that a power source would be the only thing they have in common but....there I go thinking again.

firstbase said:

Thanks, Bill. At some point, I will remember "simple things first". I would think that a power source would be the only thing they have in common but....there I go thinking again.

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A power source and a ground connection are the only things in common.

We had an interesting thing happen recently where the upper helm gauges failed on a vessel near me.

Article here: Lightning Strike series Summary (parts 1 and 2) article on janice142

Basically lightning messed up the gauges and start key topside. The diagnosis was flawed due to my hubris. I had rewired, traced and identified everything at the upper helm so OF COURSE it still should be correct, eh? Well, no. Not if there's a storm and lightning strikes.

Fortunately this was a minor brush and damage was limited. I'm of course hoping yours is simply a ground wire. That's the usual cause of wiring problems. Good luck.

The article describes my mistakes, and clues missed.

We had this recently on our GB and what I found was that GB liked to have a common ground bolt for some of the wiring (mine had two) and everything was just dog piled up on there with multiple connectors, after 50 years of vibration I lost one ground lug that fed the fly bridge gauges. Because they use a double gauge sender to feed both gauges with one sender weird stuff happens, downstairs gauge was affected as well. The common ground in ours was under the dash at about the level of the bottom of the wheel on left.

My first thought was bad ground. For some reason when ever I have an electricity related problem it’s always a bad ground.

Marinex said:

We had this recently on our GB and what I found was that GB liked to have a common ground bolt for some of the wiring (mine had two) and everything was just dog piled up on there with multiple connectors, after 50 years of vibration I lost one ground lug that fed the fly bridge gauges. Because they use a double gauge sender to feed both gauges with one sender weird stuff happens, downstairs gauge was affected as well. The common ground in ours was under the dash at about the level of the bottom of the wheel on left.

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Thanks for the helpful hint! I have been traveling and haven't looked into it yet but will this week. There are worse adrenaline-pumping, sinking feelings in this world but looking down to see 0 oil pressure is right there with them!