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[GMCnet] What I found out about my LP gauge/wiring [message #316666] Wed, 26 April 2017 23:23 Go to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale
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Re: [GMCnet] What I found out about my LP gauge/wiring [message #316693 is a reply to message #316666] Thu, 27 April 2017 11:35 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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BobDunahugh wrote on Wed, 26 April 2017 23:23
Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale
To check the sender, you need to measure the resistance between the screw where the terminal attaches and ground. Like I said in a previous post, I think it is a standard 0 - 90 ohms. Half full would be about 45 ohms. I could be wrong, but if there is gas in the tank, there should be some resistance.

I am reconnecting my monitor panel wiring where a PO cut the wires and threw the monitor panel in a box. Dunno why the wires had to be cut, the connector would have tucked into where he had the loose wire bundle (shrug). I am trying to figure out how the gauges work. My first guess is that they act like ohmmeters (ammeters with a series resistance). When you push the button, it powers the ohmmeter. That measures the resistance across (current through) the sending unit. When you push the button, that puts the gauge in series with the sending unit, with 12VDC pushing on one side of the gauge/meter, through the sending unit, to ground.

The LPG tank itself needs to be grounded to complete the circuit, because the sender grounds to the tank. You need continuity from the monitor panel connector LPG lead to the LPG sending unit. Expanding out from that, you should see the same resistance at the monitor panel LPG lead of the panel connector (to ground) that you do at the sending unit (to ground).

Lots of things can go wrong. Corrosion at the connectors, broken wire, shorted wire, stuck float, ungrounded tank. You get the idea.
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316694 is a reply to message #316666] Thu, 27 April 2017 11:49 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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BobDunahugh wrote on Wed, 26 April 2017 23:23
Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale
Your symptoms indicate a discontinuity or high impedance in the circuit. Corroded connector, ungrounded tank, broken or disconnected wire, float stuck at full. Something like that. Sending unit to ground should have some resistance, but not large (~45 ohms at half full?). Resistance to ground of the end of the LPG wire at the monitor panel connector should be almost identical to the reading at the sending unit.

I guess I am saying to check resistances and continuity of wires and sender instead of volts. Once you get the wiring right, if the sender is working right, and the gauge doesn't work right, suspect the gauge.

Unfortunately, I can't tell you the right resistance readings for the sender. I am just guessing the "standard" 0 - 90 ohms (0 for empty and 90 for full).
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316701 is a reply to message #316666] Thu, 27 April 2017 14:17 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
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BobDunahugh wrote on Wed, 26 April 2017 23:23
Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale
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Bob,
The 78 Royale utilizes a standard 0-90ohm balancing coil fuel gauge, There are three terminals on the back of the round 52mm (2 1/4") gauge. The one marked (+) is 12v power from the ignition switch source. The one marked (-) goes to the sending unit in the tank. The third one, usually located between and below the other two is a ground. (not usually marked) The ground at the gauge is essential if you want the gauge to work. Without it, the needle will deflect either full or empty (depending on how it is wired), with no in between deflection indicating fuel level. Check and make sure your gauge is wired properly.


Larry Smile
78 Royale w/500 Caddy
Menomonie, WI.
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316711 is a reply to message #316694] Thu, 27 April 2017 16:01 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
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You are correct. It is a 90 ohm sending unit.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316715 is a reply to message #316711] Thu, 27 April 2017 18:02 Go to previous messageGo to next message
Adrien G. is currently offline  Adrien G.   United States
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The sending unit resistance is 90 Ohms will read empty.
Full reading will be 0 (zero) Ohms.
If the sending unit is stuck inside. Remove the tank to shake it and check ohms
or lightly drop one end to again shock the sender loose, check ohms, sometimes it works

I had a fuel tank sender that was stuck, with the tank full of fuel, a rubber hammer and a couple
of hits on the bottom, it's back to a working sender.



Adrien & Jenny Genesoto 75 Glenbrook (26-3) Mods LS3.70 FD / Reaction Sys / 80mm Front&Intermidiate / Hydroboost / 16" Tires / Frame Rebuild / Interior Rebuild Yuba City,Ca. Text 530-nine-3-three-3-nine-nine-6
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316908 is a reply to message #316701] Mon, 01 May 2017 15:29 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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Larry wrote on Thu, 27 April 2017 14:17
Bob,
The 78 Royale utilizes a standard 0-90ohm balancing coil fuel gauge, There are three terminals on the back of the round 52mm (2 1/4") gauge. The one marked (+) is 12v power from the ignition switch source. The one marked (-) goes to the sending unit in the tank. The third one, usually located between and below the other two is a ground. (not usually marked) The ground at the gauge is essential if you want the gauge to work. Without it, the needle will deflect either full or empty (depending on how it is wired), with no in between deflection indicating fuel level. Check and make sure your gauge is wired properly.
Larry,

Can you tell me how the gauge works? Is it a voltmeter or an ammeter or an ohmmeter? I got an LPG gauge that has nothing connected to it and it reads HALF full (or half empty, depending on your outlook on life...). The fresh water gauge does the same thing. How/why do they decide to go to half scale for no reason?
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316921 is a reply to message #316666] Mon, 01 May 2017 17:19 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
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I could try to explain it myself, but instead, take a look at this link, and scroll down to "Fig. 9.33. Typical instrument circuit using balanced coil".

http://what-when-how.com/automobile/fuel-gauges-automobile/

and

Fig. 9.34. Schematic of the sending unit


Larry Smile
78 Royale w/500 Caddy
Menomonie, WI.

[Updated on: Mon, 01 May 2017 17:22]

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Re: [GMCnet] What I found out about my LP gauge/wiring [message #316925 is a reply to message #316921] Mon, 01 May 2017 17:56 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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Larry wrote on Mon, 01 May 2017 17:19
I could try to explain it myself, but instead, take a look at this link, and scroll down to "Fig. 9.33. Typical instrument circuit using balanced coil".
http://what-when-how.com/automobile/fuel-gauges-automobile/

and

Fig. 9.34. Schematic of the sending unit
Thanks. I see how it works. I would think they would point to "E" when not energized. But why would a gauge stop working, or "settle" someplace arbitrary when it gets old, like half or 3/4 or 1/4 full?
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316935 is a reply to message #316925] Mon, 01 May 2017 19:36 Go to previous messageGo to next message
kstockwell is currently offline  kstockwell   United States
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my waste tank reads E, when I push the button to energize it it moves below E to around 7 o'clock.

I wish it worked but it's not worth any risk breaking things to replace it.



1978 Kingsley Putney VT
Re: [GMCnet] What I found out about my LP gauge/wiring [message #316943 is a reply to message #316666] Mon, 01 May 2017 20:43 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Larry Weidner told me there were three terminals as you did. I showed him the panel in my 78 Royale. And my extra broken panel out of a Royale. Both have just two terminals. Bob Dunahugh





Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale
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Re: [GMCnet] What I found out about my LP gauge/wiring [message #316946 is a reply to message #316943] Mon, 01 May 2017 21:29 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
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Bob,

Ahhh....maybe yours is the "Fig. 9.32. Typical instrument circuit using thermostatic heating" See then Fig 9.32 the first illustration at this link.

http://what-when-how.com/automobile/fuel-gauges-automobile/

May mean you need a thermostatic heating style gauge.


Larry Smile
78 Royale w/500 Caddy
Menomonie, WI.

[Updated on: Mon, 01 May 2017 21:32]

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Re: [GMCnet] What I found out about my LP gauge/wiring [message #317387 is a reply to message #316666] Thu, 11 May 2017 13:34 Go to previous messageGo to next message
Hoosier is currently offline  Hoosier   United States
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Quote:
Gauge shows full all the time. Pushed the LP gauge switch. Had 12 volt on both the terminals on the back of the gauge. ( Both the red, and white wires are not connected to the tank sender. ) The white wire at the tank, But not connected to the tank sender. Is a true ground to the body. Next I need to engage the LP gauge switch to see what voltage I have at the red power wire at the tank. Shouldn't the voltage at the tank be lower? If I have power at the tank. Attach the ground to the ground terminal on the tank. It should work. If not. I need to check continuity in the sender. Bob Dunahugh 78 Royale


Bob, The sending unit on the end of the tank is removable with 2 small screws, top & bottom. It can be removed with no danger of losing propane. After removing the sender you can move the needle with a bar magnet, as it is magnetically connected to the mechanical sender inside the tank. Make temporary connections after you move the needle and check results on the panel. My panel gauge has 2 wires on it and reads full until I press the switch; then reads close to where I have the needle set. Sender is near 0 ohm empty, 90+ full.
When I first got my coach the circuit did not work. The tank was empty so I removed the sending unit which being mechanical and worn was physically stuck. A little manipulating and it freed up. The rubber hammer mentioned earlier might have worked. Probably without the trouble of removing the tank. I haven't driven mine since the repair - as the mechanical sender bounces continually when propane is in the tank, wear has to become an issue.


RayBechtel Roxboro, NC 1976 Royale
Re: [GMCnet] What I found out about my LP gauge/wiring [message #317410 is a reply to message #316943] Thu, 11 May 2017 20:52 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Ray. This Royale sat from Oct of 1995 to Oct of 2015 next to a corn field. The stuck idea is sounding more probable all the time. My problem now is that I'll have to take an entire kitchen cabinet out to check the idea. And the tank is full. So now the hammer idea.

Bob Dunahugh 78 Royale
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Re: [GMCnet] What I found out about my LP gauge/wiring [message #317411 is a reply to message #317410] Thu, 11 May 2017 21:05 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
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Bob,

I know this is heresy for someone as determined to achieve perfection as
you are, BUT: If the hammer idea doesn't work, why don't you just settle
for knowing that the tank is "more than big enough"?

With the tank holding more than 'most anyone uses in a year, just get it
refilled before every trip and forget the gauge. You'll probably find that
even if you're on a months-long trip, a monthly refill will be more than
adequate. After a couple of refills, you'll have a good standard of time
vs gallons. I'd guess you'll use less than 5 gallons per month.

JWID,

Ken H.


On Thu, May 11, 2017 at 9:52 PM, Bob Dunahugh wrote:

> Ray. This Royale sat from Oct of 1995 to Oct of 2015 next to a corn field.
> The stuck idea is sounding more probable all the time. My problem now is
> that I'll have to take an entire kitchen cabinet out to check the idea. And
> the tank is full. So now the hammer idea.
>
> Bob Dunahugh 78 Royale
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: [GMCnet] What I found out about my LP gauge/wiring [message #317439 is a reply to message #317410] Fri, 12 May 2017 09:55 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Ken. Good point. Good idea. My deep personal problem is that something that's not working. And me not fixing it. Drives me CRAZY. The bright side is that I can get the LP tank topped off about 3 miles from my house.

Bob Dunahugh 78 Royale
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Re: [GMCnet] What I found out about my LP gauge/wiring [message #317441 is a reply to message #317439] Fri, 12 May 2017 10:08 Go to previous messageGo to next message
James Hupy is currently offline  James Hupy   United States
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I heat my shop with propane, and have 200 gallons of storage. My propane
tanks have a wireless transponder that tells my delivery driver when they
are getting low. When he shows up, if my coach is low, he fills it, too.
EZ-PZ.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On May 12, 2017 7:56 AM, "Bob Dunahugh" wrote:

> Ken. Good point. Good idea. My deep personal problem is that something
> that's not working. And me not fixing it. Drives me CRAZY. The bright side
> is that I can get the LP tank topped off about 3 miles from my house.
>
> Bob Dunahugh 78 Royale
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Re: [GMCnet] What I found out about my LP gauge/wiring [message #317450 is a reply to message #317439] Fri, 12 May 2017 11:58 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
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BobDunahugh wrote on Fri, 12 May 2017 09:55
Ken. Good point. Good idea. My deep personal problem is that something that's not working. And me not fixing it. Drives me CRAZY. The bright side is that I can get the LP tank topped off about 3 miles from my house.

Bob Dunahugh 78 Royale



That is what I need. I have plenty of things around here that need fixing. Stop by anytime.

I fill up my tanks about every 3 years. My gauge quit about a year ago and it drives me nuts not being able to see how much I have.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] What I found out about my LP gauge/wiring [message #317455 is a reply to message #317450] Fri, 12 May 2017 13:14 Go to previous message
Ken Henderson is currently offline  Ken Henderson   United States
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I guess I'm just not as paranoid as you guys! I've only got a 7.6 gallon
tank, which needs filling about twice a year -- maybe. The gauge does
work, but I don't really trust it, so I fill it about every second trip --
with 4 gallons or so. That little bit of LPG is enough to keep the
refrigerator running during all of our travels; 120vac in the camp grounds
handles the rest. That's the only use since SHE never lights the stove and
I removed the furnace.

Ken H.


On Fri, May 12, 2017 at 12:58 PM, Ken Burton wrote:

> BobDunahugh wrote on Fri, 12 May 2017 09:55
>> Ken. Good point. Good idea. My deep personal problem is that something
> that's not working. And me not fixing it. Drives me CRAZY. The bright side
>> is that I can get the LP tank topped off about 3 miles from my house.
>>
>> Bob Dunahugh 78 Royale
>
> That is what I need. I have plenty of things around here that need
> fixing. Stop by anytime.
>
> I fill up my tanks about every 3 years. My gauge quit about a year ago
> and it drives me nuts not being able to see how much I have.
> --
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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