Upside down fuel gauge.
Discussion
Blue 30 said:
Taking things slowly... I think the first thing you should do, is back track, and establish what you (or someone) has done to cause the change.
IE. Sender wires off, back on. Tank sender swop. Messing around with the dash wiring.
Or did it just happen ?
I basically connected the Jag in tank pump/level sender to the TVR gauge while the pump/level sender were out of the tank. Switched the ignition on and moved the level sender through its range several times, observing the TVR gauge. The Jag sender would normally connect through it's computer and probably operate at 5v. IE. Sender wires off, back on. Tank sender swop. Messing around with the dash wiring.
Or did it just happen ?
Okay...
So the most likely reason for the reverse reading is, that the Jag sender goes from low to high resistance (as the fuel level rises), whereas the original sender goes from high resistance to low.
Don't get concerned what voltage the Jag system ran on, as its the sender resistance range that's important.
From what others have said, the original is around 230ohms > 0ohms as the tank fills. So the Jag needs to be close to that, especially as it heads towards 0ohms, as its that reading that gives the 'full' reading. (Even though it works in reverse)
If you can prove the Jag unit is low resistance at empty, heading to high resistance. Then its a matter of access. To tap into the opposite end of the rheostat to rewire it.
Oh, there is a simple fix (but slighly costly), as there is a little black box that does gauge to sender matching. Sorry I don't know any brand names, but Google should reveal all, or try CBS.
T.
So the most likely reason for the reverse reading is, that the Jag sender goes from low to high resistance (as the fuel level rises), whereas the original sender goes from high resistance to low.
Don't get concerned what voltage the Jag system ran on, as its the sender resistance range that's important.
From what others have said, the original is around 230ohms > 0ohms as the tank fills. So the Jag needs to be close to that, especially as it heads towards 0ohms, as its that reading that gives the 'full' reading. (Even though it works in reverse)
If you can prove the Jag unit is low resistance at empty, heading to high resistance. Then its a matter of access. To tap into the opposite end of the rheostat to rewire it.
Oh, there is a simple fix (but slighly costly), as there is a little black box that does gauge to sender matching. Sorry I don't know any brand names, but Google should reveal all, or try CBS.
T.
Blue 30 said:
Sorry Mike.... I've just realised you haven't asked how to correct the problem.... Drrr 
T.
No worriesT.
I have looked at most of the 'how to correct this' scenarios
I couldn't see how to gain access to the rheostat wiper connections and thought the little black boxes were
no better than re-stickering the gauge. That cost me nothing (well maybe a pint when I next meet the chap on Saturday)
It matches and looks very like the original temperature gauge too
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