What I found out about my LP gauge/wiring

Bob Dunahugh

New member
Sep 17, 2012
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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
 
> 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.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
 
> 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).
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
 
> 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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> Unsubscribe or Change List Options:
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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
78 Royale w/500 Caddy
Menomonie, WI.
 
You are correct. It is a 90 ohm sending unit.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
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.

--
”When we avoid the mistakes we might have made, we sometimes make the mistakes that we might have avoided.”

Adrien & Jenny Genesoto
75 Glenbrook 26-3
Yuba City,Ca. Text 530-nine-3-three-3-nine-nine-6
 
> 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?
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
 
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".
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
> 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?
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
 
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
 
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
 
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
 
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
 
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.

> 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. 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
 
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

> 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
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> 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
 
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.

> > 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.
> --