Fuel Gauge : Never moves, light always on

New to the Forum -
XK150 Fuel Gauge never moves, light always on.
I have searched the archives and cannot find anything, although I have seen this problem before.
I would love to hear any advise
Thanks in anticipation.

Could be that the in-tank float is full of fuel, so sunk down to the bottom of the tank. New sending units with new floats are readily available.

The fuel gauge sender rheostat and the low fuel light indication are on entirely separate circuits. The light is operated by a simple switch in the sender when the float gets to almost the bottom of the tank and the symptoms described point to the float being permanently at the bottom of the tank.

DaveXK’s suggestion is by far the most likely explanation although there are other possibilities. The sender is fixed with six 3BA screws. It’s not a big job to pop it out of the tank and see if the float is perforated. If all was well before the fault occurred I would try to repair/replace just the float. New senders are notoriously unreliable.

Don’t forget to have a new gasket to hand.

Shropshire, UK

Are the two wires to the sending unit connected to the correct terminals?

“never moves”. from where, empty or full?

Fuel Gauge Testing


BTW, I just had my dead 120 fuel gauge repaired for $130, West Valley Instruments in CA. Good prices, fast service.

Might be mix wire connection. On XK a bad tank ground to frame will cause no reading on fuel gauge. #19 green/yellow is low fuel light, #24 green/black is fuel level gauge. If you jump #19 green/yellow to ground at tank sender the light illuminate. I you jump #24 green/black at tank to ground fuel gauge should read full. Fuel gauge at dash has three connections, #17 green power (I) from ignition,#19 green/yellow is low fuel light ®, and other(T) fuel level. hope this helps

Actually, what happens if the wires on the sender are switched round can be quite confusing. Assuming that everything else is correct and this is the only fault, what you see depends on the position of the float. If it is above the minimum level, the gauge reads full or above and will continue to do so until the float gets to the empty end when it will suddenly read empty. It may flick between the two ends of the scale on the cusp.

The low fuel light will either be completely extinguished or will start to glow dimly as the level of fuel falls and the float descends. Even with the tank empty it will not be at full brilliance.

If the sender does not find a ground via the tank (on my car there is a separate black wire from an eyelet under one of the fixing screws) the gauge will read full, not empty as is the case with any open circuit on the T side of the circuit.

It’s counter intuitive, I know, but it’s just the way the system works.