Gauges powered off of accessory switch

[jclint08]

Starting to go through the rats nest of electrical wires previous owners installed on my boat & have a question. The water pressure & temp gauge get powered by an accessory switch on the console. Not sure yet if speedometer does as well, fuel gauge is disconnected so unsure their also. Shouldn't all of my gauges receive their power from the ignition when it is turned on? Or is that how they were wired from the factory?

I am having to remind myself to turn on & off this accessory switch when I get on & off the water. Without the key even in the ignition, gauges still work when the switch is turned on. Anyone else happen to have their gauges powered this way? As I mentioned, underneath the steering console is a rats nest of wires, wire nuts & electrical tape. I am slowly trying to put everything back to original as best I can.

Boat is a 17' 1986 Fiberking Starfire with 1986 150 HP Mercury Blackmax.

 

[Pmccraney]

Re: Gauges powered off of accessory switch

I am no pro by any means... (in fact, I just posted my recent cry for help)... However, the way that is set up is definitely odd... I've heard of some folks wiring the gauge "lights" off a switched accessory circuit on the house battery, but never actual power to the gauges. Maybe they tried to do that, and ended up bringing power to the gauges that way... Who knows..

Since you are redoing everything anyway, I would grab your +12V from the ignition and daisy chain that power down the line of your gauges...

Some pros will surely come along after me and will give you better guidance...

 

[glenn property of pam]

Re: Gauges powered off of accessory switch

old boats get wired differently over the years to suit the owners or they just get a little screwed up on the wiring. If you have no need to check the gauges with the engine off (fuel level, battery level) then rewire them to the ignition acc wire.

p.s just remember is not a lot of wires its one wire a lot of times and you will get it sorted

 

[Silvertip]

Re: Gauges powered off of accessory switch

Why anyone does that is a complete mystery. It makes zero sense. The "I" terminal on the ignition switch powers the "I" terminal on the gauges which are simply daisy chained from one gauge to the next. Same for the grounds. The internal light for each gauge are also daisy chained but are generally powered by the NAV position of the Nav/Anc switch. Why the NAV side? Why have the instrument lights on when you are anchored? Some manufacturers wire them to the "I" terminal so they the gauges are lit any time the ignition is in the RUN position.

 

[jclint08]

Re: Gauges powered off of accessory switch

Perhaps wiring the gauges through this accessory switch was a way for the previous owner to turn on the gauge lights. Not sure.

1) Do gauges (fuel, water temp, pressure, tach, trim, volt) normally come on once ignition is turned over?
2) Do the gauge lights stay on constantly or separate "gauge lights" switch?
3) Where would the ignition accessory wire normally be found?
4) Thanks for help.

 

[Silvertip]

Re: Gauges powered off of accessory switch

Didn't I just answer those questions? The wire that powers the gauges is on the "i" terminal on the ignition switch.

 

[Don S]

Re: Gauges powered off of accessory switch

Merc had several methods of wiring instruments depending on the type of control box used. Here is a couple of typical setups they used. The first page sounds like what you SHOULD have, where you would be running off the key switch.

View attachment Inst wiring.pdf

 

[jclint08]

Re: Gauges powered off of accessory switch

Thanks Don. That's exactly the schematic I need!