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Inoperative Fuel & Temp Gages

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Sterling_Lloyd

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Looking for help in solving the sudden death of both my fuel & temperature gages on my 73.5 MGB.
They did work great, then intermittedly, now both raed "0". I have checked out wiring and no breaks discovered. Understand that the stabalizer can be a problem at times. How does one check that out for improper operation?
Also why would my O/D speedometer not register MPH when the odometer works just great?? Any clues??

Regards, Lloyd
 
The speedometer and odometer are separate devices, both housed in the same enclosure. As for the other gauges, check grounds, fuses and voltage stabilizer. Measure voltage at the gauge, preferably with an analog meter.
 
Use of an analog meter for the stabilizer output, it should be at 10.5V out. It "ticks" between off and on, "averaging" the 10.5V output and a digital meter tends to try and keep up, giving undecipherable results.
 
Google for pictures of the stabilizer so you'll know what you're looking for. It's a rectangular metal can about the size of the end of most people's index fingers. It will have spade lugs coming off of it.

Once you've located the stabilizer look carefully at the circuit board with the spade lugs coming out of it. One pair of lugs will be labeled "B", that's the switched 12V "battery" connection. Make sure that with the ignition switch on you find 12V there. If not trace wires back to the fuse box to see where you're loosing power.

The other pair of lugs on the stabilizer will be labeled "I" for the the "instrument" connections. As the DR said, you MAY be able to put a volt meter on there and find about 10V... but don't count on it. Digital meters may not detect the voltage at all or may bounce all over the place. It is best measured with an analog meter (with a needle). However, sometimes that doesn't even work.

If you find that you have 12V at the input to the stabilizer and can't detect any voltage output, it's easy to make a modern replacement. For purists I put together a PDF on how to make your own solid state stabilizer and re-package it inside the Smiths stabiliser box. See:
https://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf

However, since the stabilizer is hidden behind the dash and this should be a negative ground car, the easiest and cheapest repair is to buy a 7810 chip from a source like Mouser.com, solder flying leads to it, cover them with heat shrink tubing and attach it to the firewall. This approach will cost you more in shipping and time than the cost of the actual parts (and still cost less than a NOS Smiths stabilizer). A JPG of this simple fix is viewable at:
https://www.adocars.com/elf/v-reg.jpg
(Thanks to my friend Wes for the JPG).
 
Will a stabilizer malfunction allow the temp gauge to work while the fuel gauge reads E all the time?

Moss had a solid state stabilizer in their lastest catalog. Probably a similar setup to the 7810 mentioned above, but packaged to look like an old Smiths stabilizer. Can't remember the cost, but probably more expensive than doing it yourself.
 
Easily more.

Will said:
Will a stabilizer malfunction allow the temp gauge to work while the fuel gauge reads E all the time?
Click to expand...


Nope, *unless* the temp gauge is an ether bulb unit.
 
wkilleffer said:
Will a stabilizer malfunction allow the temp gauge to work while the fuel gauge reads E all the time?

Moss had a solid state stabilizer in their lastest catalog. Probably a similar setup to the 7810 mentioned above, but packaged to look like an old Smiths stabilizer. Can't remember the cost, but probably more expensive than doing it yourself.
Click to expand...

Unless you have a poor connection from the voltage stabilizer to the fuel gauge, your problem is most likely a sender problem. Bad electrical connections from the sender or the float being full of fuel will cause the gauge to read empty.
 
Kimberly said:
wkilleffer said:
Will a stabilizer malfunction allow the temp gauge to work while the fuel gauge reads E all the time?

Moss had a solid state stabilizer in their lastest catalog. Probably a similar setup to the 7810 mentioned above, but packaged to look like an old Smiths stabilizer. Can't remember the cost, but probably more expensive than doing it yourself.
Click to expand...

Unless you have a poor connection from the voltage stabilizer to the fuel gauge, your problem is most likely a sender problem. Bad electrical connections from the sender or the float being full of fuel will cause the gauge to read empty.
Click to expand...

Ok, that was what I was hoping not to hear, but had been suspecting.
 
Check the connectivity at the 2nd fuse from the bottom of the fuse box.
 
TR3A fuel gauge: is it possible to test the subject fuel gauge unattached to the dash panel? My fuel gauge presently reads empty with a half full petrol tank. The two wires seem to be correctly attached to the gauge. There was a second black wire connected with the green battery power wire, which I disconnected to assure that was not the problem. Anyone test a fuel gauge not connected to the instrument panel?
 
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