Been working on my Massey Ferguson 135 and I have all the lights working for the gauges but the Ammeter Gauge. It has a little socket in the back of it for a 12v 2w bulb. If I take the socket out of the back of the guage, the lights for the other guages work. They will not work if the socket is in the back of the Ammeter guage. There is also a little black wire hanging from the socket not connected to anything. I can't find anything it should be connected to. The schematic shows a wire going from there to the starter solenoid and I tried that but had sparks flying. Any suggestions? I'm kind of at a loss right now. Thanks for any help.