I have a Hatz 2L41C engine on a Haulotte 3388RT scissor lift that the alternator isn't charging due to an open diode in the exciter circuit. While diagnosing the problem I discovered a zener diode between B+ and D+ on the alternator. Machine wasn't changing when I received it so I have no idea what was done to it prior in regards to the charge system. My question is why is there a zener diode between B+ and D+? Was someone trying to make it self exciting to remedy the exciter circuit break? Is the zener diode machine specific and installed by Haulotte? Hatz wiring diagram doesn't show a zener diode at the alternator. It's a 4 wire (W, B+, D+, D-) 14 volt 60 amp alternator (Hatz # 50504200) with an external voltage regulator. Zero tech support from Haulotte in the U.S. for this machine.