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Old 02-09-2010, 12:56 PM   #1
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1999 Monaco Diplomat gauge problems

We just purchased a 1999 Monaco Diplomat 38'. I have a problem with the dash wiring. When I pull the head light swith on to either the headlights or marker lights I get a reaction on several of the gauges. When I turn the switch knob to dim or brighten the dash lights the gauges also alter. When I turn the dash lights off the gauges return to normal. Has anyone else had this problem? Just joined this group and looks like a really interesting bunch.

Any ideas would be appreciated.


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Old 02-09-2010, 02:27 PM   #2
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Welcome to The BEST forum on RV'ing.
My experience in car & truck repairs on dashes and wiring; it comes down to a loose ground wire some where under the dash or around the steering column. The ground circuit goes many places so don't be surprised if it's far from the problem. Patience is the best advice I can give you. If you remove the dash panel you might be able to use a ground jumper wire to re-connect a ground circuit between the strg/column and the light panel. If you do connect the ground and all returns to normal light wise & gauges you then have a choice- either use the extra ground wire or find the loose connection. Please let us know if you have a success outcome.
I hope this helps.
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Old 03-07-2010, 10:05 AM   #3
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Merv, you'll find more information in the Monaco forum. The Monaco's are known for grounding issues as skipwil mentions. I have a 2002 diplomat which does the same thing as yours. Originally I thought it was the lightswitch because the dimming effect wasn't linear when I turned the switch. I replaced the switch and the dimming effect is better but the guages still move significantly (voltage guage) when I turn the headlights on and turn the dimmer up to the max. The guages settle down when I turn off the dashlights.
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Old 03-07-2010, 11:40 AM   #4
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Most electric gauges work on ground resistance. If you have questionable grounds somewhere, that'll affect the gauges. What will also make the gauges 'react' is voltage drops. As the voltage to an electric gauge drops, it's reading will typically read higher (the exception would be a volt gauge!). Motorhomes have miles of wiring. Many rigs will run high-amp devices like headlights using solenoids to reduce voltage drop. However, there's still the bazillion markers and taillights connected to a mile of wiring that won't be connected to a solenoid, and the resistance can cause quite a voltage drop. Add a loose ground wire anywhere in the mix, and the gauges WILL be affected.

Our houseboat has 2 helms with full gauges, and all the gauges change depending on which ignition keys are on (or not) due to voltage drop. It's kind of frustrating, but I've gotten used to it--
2000 40' Tiffin Allegro Bus \ 2003 Chaparral 260 SSI
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
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Old 03-07-2010, 01:05 PM   #5
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I've had all the symptoms you're talking about, and it was always a ground issue.

Yours may be different, but on mine you take all of the screws that hold the dash in place, and carefully pull it out toward the drivers seat, being careful not to disconnect anything. Up against the front bulkhead there's a silver buss bar. That's all of the ground connections. Using a screwdriver, and some contact cleaner, you loosen the connections a little, spray them, and tighten them down real tight.

You've got to find out where your buss ground bar is. Mine is on the front bulkhead up under the dash. Yours may be somewhere else.

Jim Sanderson
Canada, eh?
Jim & Kate
2016 Creekside 23RKS, 2014 Ram 1500 Eco Diesel
1995 Monaco Dynasty 36', 2005 Honda Pilot
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Old 03-08-2010, 09:53 AM   #6
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Thanks guys for your interest and input. I have gone over the connections that are visible and accessible without success. It looks like my next step is to have a go at the grounding buss behind the dash. I will let you know if I have any joy.

Thanks also for the warm welcome to this most interesting forum.

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Old 03-08-2010, 03:13 PM   #7
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Just to let you know that I took a jumper wire from one of the gauge ground terminals to the main ground terminal above the brake pedal and voila! my gauges are now working perfectly. Thanks to the guys in the Monaco forum for the additional info.

Cheers from Salt Spring Island


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