Fuel tank senders

[ah]

I've got a 63L fuel tank with the 2 senders,one is for empty to half full and the other half full to max full, which is which?

[Brianmoooore]

I've got a 63L fuel tank with the 2 senders,one is for empty to half full and the other half full to max full, which is which?

I think you've got a little confused here.
The one on the right is identical to that fitted to the smaller tank, and incorporates the low fuel switch. The one on the left is electrically identical to the RH one, but doesn't have a low fuel switch.
The smaller fuel tank has a small metal pipe connecting the bottom of the two halve of the tank together, so the fuel level in each half tends to be the same, and only one sender is needed.
The 63l tank does not have this balance pipe, so the fuel levels can be different in each half, hence a level sender is needed each side. The two are connected in series, so the combined reading gives the sum of the fuel in each half.
Because the empty resistance of each sender is around 40 ohms or so, empty for a small tank is 40 ohms at the gauge, and 80 ohms for the larger tank, so different fuel gauges are needed, one reading half of the other.

[ah]

Cheers for that Brlan,I should have given you info,when my tank is quarter full or lower the fuel gauge needle has mind of its own and the low level warning light has stopped working,so my question is which sender needs changing?

[Brianmoooore]

If you're sure that the fuel low level switch isn't working (it comes on with the needle much lower than most think), then it's the RH sender, since that's the one with the switch. Most of the faulty ones I've seen have large dents in the aluminium tube, caused by someone, at some time, trying to remove the pump assembly without removing the sender first.