BMW Repair: 1987 e30 cabrio fuel guage, fuel gauge, fuel sending units

Question
Hello,  I recently bought a 87 e30 cabrio m3 replica.  The previous owner replaced the cluster with a e30 m3 cluster. With the m20 2.5 engine still in the car I replaced the cluster with a e30 325i cluster. My problem is the fuel gauge reads 1/2 when the tank is empty but the low fuel light turns on, and reads full when the tank is full. The cluster I put in is from a 89 e30 325i, my car was built 7/87.  I've read the gauge is a different part number in the cluster because 9/87 and up uses 2 fuel sending units, which would add more resistance to the circuit.  If this is correct can I just change the gauge in the cluster with a pre 9/87.  by the way the m3 cluster did the same thing.

Answer
The fuel gauge in the early e30 does have a different number than a later one, due to the wiring connection being a bullet design rather than the spade terminals of the early models.The sending unit,which is easily removed by loosening the 4 nuts.If all the wiring looks good,having the correct sender should work as you stated both problems occur with both units.The correct sender for your car is about $100 from Bavarian Autosport 1-800-535-2002