Bugeye fuel gauge

[Rut]

I'm in the process of testing my gauges and I've got a head scratcher on my fuel gauge. I have a Bugeye fuel gauge fresh back from restoration at Nisonger and a good sending unit (and I hope proper) that looks and tests to be in great shape. It is wired up per this wiring diagram and the sending unit is connected to the green-black wire in the harness. When I power up and the key is in the on position the fuel gauge pegs out on full no matter what position the sender is in or even if the sender is connected to the harness. Can anyone help me?
Thanks, Rut

 

[Rhodyspit75]

Hard to be sure but from your picture the ground ring connector appears to be touching the terminal.

 

[Rut]

Hard to be sure but from your picture the ground ring connector appears to be touching the terminal.

Thanks, but the ground rings are a good 1/2" above the terminals...wish that was it!
Rut

 

[dklawson]

I cannot tell from your picture or the schematic but I assume you have the following connections on the gauge.

B & T will be stamped on the gauge case next to the terminals.
B = Battery = green wire from fuse box
T = Tank = green/black wire from sending unit.

The fuel gauge case must have a good ground. I assume one of the black wires on the gauge mounting stud is grounded on the other end.

The magnetic gauges work "backwards" to the later bimetallic gauges. The magnetic gauges will read full (or above full) when the green/black wire is disconnected (infinite resistance). A first test for you would be to connect a jumper wire between the "T" terminal and the ring terminal ground. If the gauge goes to "E" or below, there is a problem with the sending unit, the sending unit ground, or a break in the green/black wire.

Your second test would be to ground the green/black wire at the sending unit. If the gauge goes to empty, that says the problem is with the sending unit or sending unit ground.

 

[markberry]

try this link. it's an excellent tutorial on the fuel gauge system.
https://mgaguru.com/mgtech/electric/fg_01.htm

 

[Dan Ka]

Is the tank itself grounded? See Barney Gaylord' lengthy FG info at https://mgaguru.com/mgtech/electric/fg_02.htm

Dan

 

[smaceng]

Two common problems regarding fuel gauge installation: Making sure the gauge case is grounded, and making sure the sending unit is grounded. Because of the gasket used to installed the sending unit and the possibility the screws do not ground the sending unit to the tank, I run a wire directly from the sending unit screws to a good ground. Good luck
Scott in CA

 

[Rut]

Ok, had to step away and go for a ride in the MGB to clear my head. Gauge is out of the dash, jumper ground connecting the ground wire, mounting stud of gauge, and base of sending unit. Plugged sending unit into green wire with black tracer and gauge pegs out full. Disconnected from green/black and touched sending unit green/black to T connection and everything works as it should. The green/black wire for the sending unit in the boot is a lighter shade of green than the green/black wire mounted to the T connection of the gauge and I have both dark and light green/black wires not connected to anything where the harness goes thru the firewall...should they be connected?

 

[dklawson]

You asked if the green/black at the sender should be connected to the one at the gauge. Probably.

Green/black is exclusive to fuel related circuits. See the web page linked below for a summary.
https://www.mgexp.com/article/lucas-colours.html

Were I you, I would look for a place these two wires should be connected to each other. As a minimum you should check for continuity from end to end for the fuel gauge green/black and the sender green/black wire.

EDIT: Incidentally or coincidentally, I met Barney Gaylord (the MGA Guru) last weekend at a car show. He is a very interesting and talkative guy.

 

[Rut]

Doug,
Thanks...everything works as it should when I jump it, but I'm unsure if I have the correct green/black wire attached to the sender. This is a new harness and the color codes are the same, but at the T connection on the gauge the wire is dark green with 2 black stripes and at the sender it's a lighter green with 2 black stripes. When I trace the wires they end up at the point where the main harness goes thru the bulkhead if I can rely on the color code...it just seems odd that you would connect 2 different shades of green at that location. I'll break out the meter and see what truly goes where.
Rut

 

[Rut]

Reporting back that I jumped the dark and light green with black stripe and connected the gauge and sender to their correct wires and everything works perfectly! Thanks for all the help!
Rut

 

[dklawson]

That's great !

I cannot explain the mixed shades of green/black in the harness or why it is not a single wire.

 

[Bayless]

That is strange and confusing. Light green was used in some more complicated harnesses but I don't remember what for. Nice job diagnosing though.

 

[dklawson]

You are right... it is strange. Looking at the color code link I posted earlier, light-green/black is listed as being for electric windscreen spray pumps. Not something likely to be found on a car from about 1960. Maybe they accidentally grabbed the wrong spool of wire or ran out of the green/black.

 

[Paul McGuffin]

I’m sure I am a little late here, but if you develop a fuel tank leak, when you top the tank with gas, it’s usually the little screws holding the sending unit in. This time, I made sure a put some gasget seal around the threads. I once used plumber’s white tape on a VW tank that was leaking at the mounting screws. As for the white plumber’s tape, I put it on my trans and differential drain plugs. they never drip now.
PM