fuel guage sending unit

[philman]

on my "new" b-gt the fuel guage is inop. while trying to figure out what is wrong i found that the sending unit only had one wire to it with about 10 volts. no wire to the other terminal. Is the blank terminal supposed to be grounded, or am I missing part of the wiring harness? I have a wiring diagram, but even with my reading glasses the symbology is too small to read. I guess i'm getting old.

 

[kennypinkerton]

It's grounded throught the fueltank shell. You probably have a corroded connector along the way from the wire to the guage. You can check the guage (or wiring connections) by grounding the sending wire to the chassis... it should move to full.

 

[kennypinkerton]

Or... you said it has a 2 prong connection at the sending unit? One of them should be grounded.

 

[jlaird]

I would try a good ground on that extra terminal, just a test you know.

 

[philman]

sorry, i guess i wasn't too clear. the sending unit has two prongs. one has a (?)green wire to it with about 10 volts with ignition on (stabalized +12??), the other has no connection. it got late, cold and dark so i put it up for the day. i'll try grounding the green wire and see what happens.

i was proud of my self for getting the mufflers on right. it only took two tries. new pipes from the vendor have longer pipes that need to be trimmed.

 

[Kimberly]

https://www.advanceautowire.com
The above link has easy to read wiring diagrams available, they can also easily be enlarged.

 

[DrEntropy]

DO NOT ground a GREEN wire!!! There ~should~ be a green/black one to the sender, and a black one too. That's the ground. 10V at the sender is correct. Powered thru the gauge.

 

[kennypinkerton]

eeeekkk!!!!!!!!! I'm sorry! I'm giving out bad info all over the place. /ubbthreads/images/graemlins/blush.gif I've always been told to do that. maybe it's just my late model MG that you can do that on.

 

[DrEntropy]

NONOOO Kenny! Tying the two ~sender~ wires together should peg the gauge at "FULL"... but a solid GREEN wire is a direct feed from a fuse generally. The green-with-black tracer is a 10V feed from the gauge (bi-metal or inductance) and meant to sense resistance to ground... you're safe.

"GREEN" was what I reacted to.

 

[kennypinkerton]

Oh, whew! I've done it a dozen times, but mine only has the one wire going to the sender - grounded to the tank internally.

 

[DrEntropy]

They got "modern" after '75-ish. /ubbthreads/images/graemlins/jester.gif

 

[jlaird]

Durn, you scared me for a sec as well Doc. I heard the shout from here.

 

[kennypinkerton]

Heck, I can still hear the echo... /ubbthreads/images/graemlins/grin.gif

 

[DrEntropy]

...he said "green" Jack... I ~hate~ to see th' smoke.

You're close enuff to hear that?!?! /ubbthreads/images/graemlins/jester.gif

 

[piman]

Hello all,

some car like my Triumph have two terminals on the fuel sender, one is the potentiometer to the gauge, the other is a low fuel level switch and brings on a warning lamp.
If it is a ground terminal it should be obvious as they are notmally spot welded to the sender body, if a switch there will be an insulator between the body and terminal.

Alec

 

[dklawson]

Like Alec said, some Smiths senders even going back to the mid 1960s do have a low level switch. The terminals usually have a "letter stamp" next to each spade lug. I'll have to look tonight to see what each is supposed to be. I don't remember seeing those on MGBs though.

 

[DrEntropy]

To the best of my knowledge MGB's never had a "low fuel" light.

This thread is a bit timely here: Thought I had a viable "spare" sending unit. Coil in the one on the car has a shunt which has it never going below 1/2 tank. Turns out the "spare" has a similar problem at 1/4 tank... RATS! Gauge works perfectly with a spare from the Elan but I ain't about to cob that'n. Anybody have a working "six-holer" MGB unit they want rid of? /ubbthreads/images/graemlins/devilgrin.gif

 

[dklawson]

As the good DR said, I haven't seen the sending units with a low fuel warning connection on BMC cars.

I checked one that I have. If you ever come across a sending unit with three terminals, the ground is obvious, the terminal stamped "T" is for the TANK, the one stamped "W" is for the WARNING light.

 

[DrEntropy]

I spent most of 'today' tryin' to get a gas gauge to show "E" as the INDICATED time to fill up. We ~KNOW~ when it's full. Trick is knowing when it's EMPTY!!

DKLawson has an *excellent* tretise on how to determine whether or not the sending unit is tellin' ~TRUTH~!

 

[kennypinkerton]

Always fill up every 100 miles and you can't go wrong... unless you didn't actually "fill it up"... which is a whole other lesson to learn with MGB's. /ubbthreads/images/graemlins/smirk.gif