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Monitor Panel Problem [message #250561]

Sat, 24 May 2014 20:03

SThornbg

Messages: 127
Registered: September 2011

Karma: 0

Senior Member

Once again, I need electrical guidance........... '77 Palm Beach

When I activate the monitor panel I get the following - LP gauge remains at zero where it always resides even with a full LP tank; Volt meter moves to 13+ volts with the smart charger connected; the water tank gauge goes from zero to below zero and the holding tank gauge goes from zero to below zero. The switch appears to be functioning as the panel lights do turn on.

I have been told this is probably a grounding problem. I just put a fresh ground wire from the aluminum panel beneath the water pump to one of the mounting screws on the water tank sending unit - no improvement. With the panel switch turned on, voltage across the water tank sending unit is about 8.5.

Both the water tank and the holding tank are empty, but the gauges act the same with fluid in the tanks.

Any suggestions are appreciated.

Steve Thornburg South Bend, IN 77 exPB 455 "Tinker Toy"

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Re: Monitor Panel Problem [message #250566 is a reply to message #250561]

Sat, 24 May 2014 21:03

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

SThornbg wrote on Sat, 24 May 2014 18:03

Once again, I need electrical guidance........... '77 Palm Beach

When I activate the monitor panel I get the following - LP gauge remains at zero where it always resides even with a full LP tank; Volt meter moves to 13+ volts with the smart charger connected; the water tank gauge goes from zero to below zero and the holding tank gauge goes from zero to below zero. The switch appears to be functioning as the panel lights do turn on.

I have been told this is probably a grounding problem. I just put a fresh ground wire from the aluminum panel beneath the water pump to one of the mounting screws on the water tank sending unit - no improvement. With the panel switch turned on, voltage across the water tank sending unit is about 8.5.

Both the water tank and the holding tank are empty, but the gauges act the same with fluid in the tanks.

Any suggestions are appreciated.

Steve, I've been battling the same issues with mine. Last year, I got a two for one deal on new sending units for both tanks from a former GMCer who sold his coach before installing them. I installed them and tested them as I went. Outside of the tanks, they would move the needles on the gauges, but installed, they would not, or would work intermittently. I even replaced one of the gauges with a NOS unit from Jim K. The ohm readings seem to be OK, but for some reason, I can't get the gauges to work consistently. I'm thinking too, that it might be a ground issue, but really haven't delved into it yet. What baffles me is that the light in the panel works, so that would indicate an in tact ground.

Hopefully someone can help both of us get to the bottom of this problem once and for all.

Carl Stouffer '75 ex Palm Beach Tucson, AZ. Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member

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Re: Monitor Panel Problem [message #250569 is a reply to message #250561]

Sat, 24 May 2014 21:16

Richard Andis

Messages: 261
Registered: January 2013
Location: HELL Paso, TX

Karma: 0

Senior Member

I'd start with downloading the wiring diagram from here
http://www.bdub.net/wirediagrams/

Each of those circuits work pretty much alike. 12v applied over a variable resistance. Resistance is determined by the amount of contents in its respective tank. Works exactly like the fuel gauge on vehicles of the era.

I'd first check if there was 12v going to the circuit. Then check the ground. It is possible (and probable) that all of the senders have gone bad. The diagram shows a connector you can take readings from.

Valhalla - 1978 GMC Royale rear twin [SOLD]
Walküre - 1974 VW Thing (Toad)

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Re: Monitor Panel Problem [message #250574 is a reply to message #250569]

Sat, 24 May 2014 21:51

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

These systems use a standard AC/Delco air core gauges. They use a nominal 12V supply and balance the gauge resistance with a known resistance inside the
gauge itself. They all read sender as low or empty at low resistance (~3Ω) and high or full at high resistance (~90Ω).
So, if the needle is pinned low, look for a short to ground in the sensor lead. If it is high, the system has an open.

NEVER put 12V to a sensor, it will be destroyed instantly.

Now that you know this, look for bad grounds first as they are easier to find. Do not hesitate to run a new ground wire to a known good ground. If a sensor lead is shorted to ground, look in the places where is passes through joints with metal on one or both sides. It is not uncommon for the insulation to get crushed or worn by vibration.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

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Re: Monitor Panel Problem [message #250647 is a reply to message #250574]

Mon, 26 May 2014 10:00

SThornbg

Messages: 127
Registered: September 2011

Karma: 0

Senior Member

OK, water tank is full, fresh ground wire to the aluminum body, monitor panel switch on, the gauge goes negative to the peg. Voltage from the yellow wire to ground is 8.5 volts - I did not remove the yellow wire from the sender to measure the voltage. Looks to me from the wiring diagram that the yellow wire should be carrying 12 volts from the purple wire that comes from fuse #3.

LPG gauge holds steady at Empty and the gauge on the tank reads empty - again a fresh ground on that one.

I have not looked at the holding tank as yet. It is empty and that gauge on the monitor panel makes a negative move when the switch is turned on.

???????????????

Steve Thornburg South Bend, IN 77 exPB 455 "Tinker Toy"

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