Waterfoul

I have had this problem basically since I bought the boat 8 years ago. When I turn on my nav lights, all my gauges back up. That is, they all change their readings, oil pressure goes from 50 to 30, volts goes from 14 to 12, etc... Only thing that is not effected is the tach, I put that in myself several years ago. And when I turn on my docking lights, everything really goes down a ways. Been pissing me off for years, but I'm not that good at chasing bad electical problems. To me it seems I have a bad ground somewhere. I have the stereo running to it's own buss bar grounded to the block and have no trouble when I turn that on with the other systems. The previous owner re-wired the entire dash when he CNC cut a custom dash panal for it (which looks awsome by the way). But I'm not sure he got the wiring totally correct.

Any thoughts on where to start???

Wally

Sounds like you answered your own question there Mike! What i would do to verify its the ground is to try and run like an 8-10 guage wire from your batt to one of the ground wires in the dash and see if it still does the same thing.
From the sound of things the previous owner may have used the ground from the stock wireing harness in the boat that goes to the engine. Try and run a new gounding block or use that other one you have for you stereo/or tach. Hope that helps.

Smitty

You definitely need to make sure that your ground is not only clean but that the wire/s providing the ground is at least equal to your power supply wire size. I would also recommend getting a higher output alternator with a smaller pulley to increase the output at all rpms. I had a similar problem and did this and it is much better now. Also the stock alt output is only about 55 amp but you can go up to around 100 amps.

Waterfoul

I've got a high output alternator already. Still does it. So I know it's wiring related. What color is the ground in the Mercruiser wiring harness??? White? Black??

gmnhra

i posted pretty much the same question a while back and got good responses...the most consistant response was the "bad Ground" response...Wallys response to use a large gauge wire direct to the battery is one of those "duh" ideas that is the perfect way to isolate if it indeed is a bad wire harness ground wire..i will try it this weekend...

i will also say that i have observed this "gauge back up" phenomenon to a certain degree on two other boats i have ridden in recently so it may not necessarily be a problem. simply a reflection on the gauges that there is a voltage drop due to current flowing to the devices turned on....

it does bug me though.....

keep us posted with your results...it may help me also!!

gary

mopower

I had the same problem with a FourWinns and it was an inadaquate ground or a loose or dirty connection some where. All I did was run a seperate ground from the battery to the instruments and it cleared the trouble. My present Formula also showed low voltage and slightly elevated temps. Had 11.5 volts to the guages and 12.5 on the back of the ignition switches. Found a dirty connection on the hot side and now volt meters match battery voltage , and temps are back down to normal. I just couldn't believe both engines were running exactly the same high temps at exactly the same time!

NASTY HABIT

all roads lead to the ground.....figuratively speaking that is ..cannot count the times I've chased down electrical gremlins only to find a poorly connected or inadiquate ground...

my wife is laughing as I type this... she has seem every time ...now when something wierd is happening with any kind of electrical gizmos I go straight for the ground wire


good luck

Waterfoul

O.K. I know all my grounds are tight and clean, I just had the motor out and redid most of the connections. No improvement at that time. So, it has to be the ground from the gauges, but I have no idea what color wire to look for. The previous owner siad he used Mercruiser/Baja color codes, so I'm not even sure what wire to chase down!!!!

But, I did get my non-functioning bilge pump to work today. Turns out the hose clamp at the pump wasn't makeing a good seal so it wouldn't pump the water past about half way up the hose. Issue solved with a little silicone and a new clamp. Now, 1100 gph out that little puppy. Which is good, cause I have a leak I can't seem to solve either!!!! If it's not one thing, it's another!!!!

Now, out to find bad grounds!!!

Turbojack

Common ground wire in a home is WHITE, Common ground wire in automotive (boat) is black. I have see some green tho. When people are saying ground what is really happening is you are having a voltage drop. When you are turning on your lights the lights are getting there ground from your dash area. The greater load on the ground wire the greater the voltage drop. Running a larger wire from motor to the gauges should solve the problem. Remember the gauge is working off the voltage difference, As you increase load on ground voltage drop increase.

I just notice on my motor home last sunday same problem. Last week when I was going to lake in rain (lights on) I thought the engine temp was a little high. On way back (lights off) is was at its normal place. Sunday went to get fuel (lights off) & temp was norma, when I got home (dark & had lights on)I was starting to worry. I then turned lights on / off, temp would go up & down 25 degrees. So problem is just not boats.

Waterfoul

I've been living with this issue for 8 years. And with my new motor I just want to know where my oil temp and pressure are, even in the dark!! So, what you're saying is that if I really want to get it right, I should run a new, larger ground wire for all the gauges, perhaps to a buss bar under the dash, to which I can run all the gauge grounds????? Man, given the dash layout on this boat, that's a LOT of work. Looks like spaghetti under there too (NOT the way I would have done it).

Oh, and the trouble shooting gun gets another notch. Figured out why my depth gauge kept turning on and off when on plane, loose POSITIVE wire at the ignition. Hit a wave, gauge beeped because it went off and came back on. Issure resolved. No more beeping.

So, that's two down, MANY to go.