Fuel and Temp Gauges (5 Viewers)

[GregFrench]

My fuel gauge and temp gauge work most of the time. When they quit, they quit at the same time. When they start working again a day or so later, it is at the same time. Where do these 2 gauges meet? Are they connected at a fuse or something? This could help me narrow down where the loose connection is.

 

[alex.t]

Check your ground. I lost my headlights, though the high beam indicator would come on in the gauge cluster. Traced it back to a bad ground.

 

[calsum2]

check your Fuse

 

[bj42turbo]

I had this prob awhile back turned out to be a common ground on top of the tank, mine is underneath had to be accessed via the inspection panel.

BJ

 

[Rocky_LC]

If the fuel tank ground is bad (i.e. curcuit is open) what does the guage read? All the way empty, of all the way full?

How does this curcuit work?

Thanks -

Rocky

PS> After my new tank was installed, my fuel guage is reading "below empty"

 

[GregFrench]

Both of my gauges read empty when they go out.

 

[fussy_cruiser]

check your Fuse

x2, had a bad one on the running lights, also disconnect the battery and take a copper wire brush to the fuse contacts, works wonders.

 

[fjwagon]

Or the problem could in the instrument cluster. Try reseating the plug. You can test the fuel gauge by shorting out the fuel sending unit output to ground. It should read a full tank.

 

[Pin_Head]

They share a fuse and the power wire circuit. Check for corrosion and bad connections from the fuse block tothe gauge. They have separate grounds, so this is not likely the cause of the problem.

 

[fjwagon]

What is not the likely problem......the connector at the instrument cluster. If the fuel gauge moves to the "full" postion, chances are good the temp gauge will work as well.

 

[GregFrench]

Or the problem could in the instrument cluster. Try reseating the plug. You can test the fuel gauge by shorting out the fuel sending unit output to ground. It should read a full tank.

Tried the plug. I know the gauges work. In fact, they both work well most of the time. Every once in a while I will look down and they will both be at zero. Then I will look down again (sometimes a day or so later) and they will both ebe working again.

I'll check the fuses. Which fuse is it? Mine are not labeled, and I have no owners manual.

 

[fjwagon]

I looked at both fsm's, 1975 and 1981, it shows the Heater 20A should be culprit on both manuals. For the 75 it effects heater, back up light switch, stop light, water gauge, temp gauge, oil pressure, and the fuel gauge.

For the 81 it effects the oil, water temp, fuel gauges, parking brake light, brake(brake fluid level.)

For an 82should be laid out like this:
15A tail
15A stop-horn
5A radio
15A Light
15A engine
20A heater
20A Turn-wiper

I'll check the fuses. Which fuse is it? Mine are not labeled, and I have no owners manual.

 

[fjwagon]

On the 75 manual, the fuse block reads, starting from the top:
tail 15A( meter pilot lights, parking lights, tail lights and licsence plate lights)

stop 20A(stop lights, horns and harard warning lights)

lighter 20A(cigearette lighter, interior lights and inspection light socket)

wiper 20A( radio Windshield wipers and washer)

heater 20A(heater blower, back-up, lights, gauges, front drive system, and parking brake warning lights)

turn 15A( turn signal lights)

engine15A(alternator, regulator (Ig. terminal), fuel cut selenoid and emission control system)

head lamp 20A (headlights)

 

[BJ42Brumby]

The Earth

Hi all,

Coming from a background of restoring minis.. I've always found when you have a weird electrical problem the first thing to do is look at the fuses. If the fuses are fine then you can bet your left bollock that it's a dodgy earth connection. Check those earths. Make them clean and bright and cover with a dab of silicon once you've reattached them. English cars used to have Lucas electrics. There's a reason they call him the Prince of Darkness. He didn't invent electricity but he invented the short circuit....

 

[cruiseroutfit]

Bump any update on this?

Oddly enough my 40 (72' harness) did this for the first time today, first and only time... both the fuel and the temp zeroed out, the oil pressure was fine. I hopped out thinking immediately it was just a fuse, played with the fuses and "tapped" the back of my cluster and they popped right back to life. Not 100% sure I fixed it by simply reseating a fuse? Mabey so?? I havn't been able to duplicate the problem.

UPDATE: - I was able to get the problem to duplicate, so I was able to pull out my multimeter and get some readouts. To my suprise my Water Temp guage is powered THROUGH the fuel sender, not off of the same fuse (such as the Oil Press.), rather the Temp guage gets its 12V power through a 3rd post on the fuel guage. I'm still trying to figure out exactly how/why it all works... the leg of the fuel guage that sends its power to the Water Temp has a "switch" of sorts that is adjustable by a very small screw on the side of the fuel gauge. When this "switch" is closed, it allows the 12V to travel through the 3rd post and into the Water Temp. Also, when closed, it allows the 12V to enter the "coil" that makes the fuel guage work. Easy enough to bypass the "switch" and run the 3rd post directly from the 12V fused source, and this in turn will power the Water Temp guage always. What is the purpose of this switch???. I'm 99.9% sure this is OEM, I've got a couple of guages this way, and 2 complete instrument clusters that are all wired completely the same in this fashion. I beleive they only used this from late 72' - mid 73', possilbly less than a 6 months? I don't have an FSM for either a 72' or a 73', so I havn't been able to see if the FSM covers the "switch" or not. Anyone have one they could check?

Pictures:

Here you can see the 3 posts, viewing from the back, the left is the 12V from fuse, the right is the from the sender, the top middle (what I call 3rd post) is the post that eventually powers the Water Temp Guage, but only when the "switch" is closed.

Close up of the fuel guage, as you can see, there is a small set of contacts, adjustable by a screw that will divert power to the top-middle post, as well as the fuel guage coil itself. Why?

 

[cruiseroutfit]

Bump for my update

 

[dfmorse]

Greg;

I'll post this here and in Kurts thread:
There may be a resister (variable) in line for the "Voltage Regulator & Fuel" gauge. If these resistor is intermittant, it could cause ur problem...

Kurt;

Here is what I've got on this so far.

My older manuals don't have the detail required to shoot this out properly. Besides, the schematics are a night mare.

However; manual 98154 gives some clues to the way this water gauge and fuel gauge are coupled inside the combination meter.

Page 12-26 show the interconnect of the two gauges, but not the internal switch u have found. There is a voltage regulator common to both gauges (2-7 volts); i.e., these two gauges want to see 2 to 7 volts (not 12 volt battery). Perhaps the third terminal is for this purpose. For example, when u turn the ignition "on", 12v is applied to the voltage regulator (inside the fuel gauge); as the fuel gauge coil begins to activate, it trips the 'switch' applying 2-7 volts to the "water temp gauge".
This may be used (the switch) as a de-load system. In other words, get the fuel gauge moving first, then kick in the temp gauge. When it kicks in is determined by the set screw.



Or, the third terminal was used as a calibration point for factory use.

...

 

[40's rock]

bump to the fuses....had same issue and a little love rub on all the fuses in the panel and bingo...little 400 grit on contacts...no more problems.

 

[cruiseroutfit]

...Kurt;

Here is what I've got on this so far.

My older manuals don't have the detail required to shoot this out properly. Besides, the schematics are a night mare.

However; manual 98154 gives some clues to the way this water gauge and fuel gauge are coupled inside the combination meter.

Page 12-26 show the interconnect of the two gauges, but not the internal switch u have found. There is a voltage regulator common to both gauges (2-7 volts); i.e., these two gauges want to see 2 to 7 volts (not 12 volt battery). Perhaps the third terminal is for this purpose. For example, when u turn the ignition "on", 12v is applied to the voltage regulator (inside the fuel gauge); as the fuel gauge coil begins to activate, it trips the 'switch' applying 2-7 volts to the "water temp gauge".
This may be used (the switch) as a de-load system. In other words, get the fuel gauge moving first, then kick in the temp gauge. When it kicks in is determined by the set screw.

That is the most reasonable thing I've heard thusfar. Though I don't think the switch I have would act as the resistor itself, rather as the voltage regulator proper, if it gets more than a certain voltage, I can see how it would drop power to both guages (via no power to the top-middle post).

...Or, the third terminal was used as a calibration point for factory use.

...

I don't think that is the case, seems the voltage regulator theory is the best yet

 

[Pin_Head]

I don't see why these gauges would need regulated power other than the chassis power that is already regulated. If there is a regulator, it isn't indicated in any of the schematics.

From what you can see in the picture, I can't see how this "switch" device would function as a VR. It seems more likely to be some way of adjusting the full scale swing of the meter.

What side of the "switch" is the center post connected to? Can't really see this well in the pictures.