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how to determine B or T terminal on fuel gauge?

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J

James_the_elder

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I have an old fuel gauge, round, 2" dia., marked "Smiths" on the face. The back of the case has 2 terminals, center threaded post for the mounting bracket and a 1/2" hole for a light socket. Does anyone have a clever way of determining which terminal is B or T? I have looked carefully and there are no markings on the case, just a small paper label printed with "050"
James the Elder
 
Try it one way then the other just holding the wires on the terminals with the gauge out and ign on. One way or the other will work.
 
Measure resistance between each terminal and the gauge case. One terminal should measure about 100 Ohms. The other... maybe 160? The terminal with the higher resistance to the case is "B", the lower resistance terminal is "T".

If neither terminal has measurable resistance to the gauge case, either it's a later type gauge OR there is a broken winding inside. If it's a later type gauge it is not compatible with the systems that do not have the voltage stabilizer. Every early gauge I've seen has "B" and "T" stamped on the case.
 
I've never seen an unmarked one either. But then I gues there are a bunch that I have not actually seen. If it is the older style, you can hold it upright, looking at the back. The B post will be to you right. Also, the B post is on the "Empty" side and the T post is on the "Full" side. Also, I believe the resistances Doug gave should be right.
 
Thanks all for your ideas. One more thing I discovered when I took off the chrome bezel and glass. The dial consists of two thin metal pieces. On the inner dial face just above the "F" there is this number
BF 2223/00 is that a clue ?
 
Yes, that is indeed a clue.

The BF #### can be used to identify where the gauge was originally used. I do NOT have the secret decoder book for part numbers. However, Googling for the part number I found the two links below.

First see eBay and look for item #290328716790 That should be the same type of gauge you have based on the part number you listed.

More importantly, visit this web page:
https://www.mgb-stuff.org.uk/fuel.htm
Search the page for "2223/00" and you'll come to a section that says the gauge you have is for MGBs made after 1967. That means it is for cars WITH the voltage stabilizer.

Look at the back of your gauge. If (excluding the rust) it looks like the back of the gauge shown in the second link above, the gauge you have is for later cars. You will notice it has two "screwdriver slots" below holes on the back of the gauge.

The back of your gauge should look like this:
https://mgaguru.com/mgtech//electric/pics/fg_289.jpg
(Thanks to Barney Gaylord for the picture).
Notice that instead of the screwdriver slots there are two additional little studs (with nuts) poking out the back of the gauge. These little studs pass through short slots. That's the type of gauge an early car without the voltage stabilizer needs.

You cannot mix the two gauge and sending unit types. The later type gauge(your BF2223/00) will need the voltage stabilizer, and cannot work with the early sending unit. The early type gauge cannot work on cars with the later sending unit and voltage stabilizer.
 
Thanks dklawson:
I think that pretty well settles it. I have a new type gauge that requires a voltage stabilizer and it won't work on my bugeye because I have no stabilizer and an old type tank sending unit. I went to www.mgb-stuff and that's the gauge that I have. Thanks for your help, at least I learned something.
 
Sorry the gauge you have isn't going to work. Just remember the rule that you never throw anything out. You might own a later Spridget or MGB sometime and want that gauge or you can trade it for what you do need.

A lot of the other BMC cars of the same period as the Bugeye would have suitable gauges. You could even use a gauge from a car like an early Spitfire. However, they will likely be marked "Jaeger" instead of Smiths.
 
However, guage faces can be changed to reflect the appropiate Bugeye or what ever face. Never throw away and old guage, think parts.

For example, Miss Agatha has a 65, I think, water/oil guage with a bugeye face.

Oh yea the needles come right off with a dinner fork to pry with.
 
Jack, 90 degree sweep temp and fuel gauge needles don't come off at all. They are thin, formed sheet metal bits attached to the inside of the gauge. The 270 degree sweep temperature gauges and the "dual gauge" needles do come off. The speedo and tach gauges have removable needles also. As you said, the gauge faces can be swapped as necessary between most 52mm gauges.
 
Yep, don't just do it. Look and think of course.
 
Sorry to hear it's not the right gauge James but do hang onto it though. All these guys are getting harder to find every day. My Prefect also has the older style and needed a gauge. The real problem was, it has a 6 volt tank unit that is different from any others I have found. The car was converted to 12 volts years ago and had a 12 volt gauge that never worked right. Finally in digging around through may boxes of old stuff, I found the right gauge. It did require significant work inside, resoldering of very thin wire, etc, but now it works like a champ.

BTW, that was some great detective work Doug.
 
Thanks Bayless. I wish I had the book with the part number cross-references in it. I'd love to see a list of gauge numbers by application AND corresponding sending units that work with them. A log like that would be very handy for one of us to own or have access to.
 
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