Got a 2-155 White with what is (according to the local alternator repairman) an alternator used on JD tractors that is a ~70 amp alternator.  Just had new brushes and regulator put on and it worked good on his bench.

The original alt on this tractor was ~50 amp, the JD alt came on the used tractor.

Gauge in tractor will show alt is charging fine with no lights on.   Turn the lights on and the guage drops way down showing that its not keeping up.

Lights are 8  HID (35w) and are rated at 8 amps @ start up.  I've been told that they use much less after they are warmed up.

Is it possible that the original wiring from the alternator is not capable of the increased capabilities of the aftermarket alt?

How would a guy go about checking the actual current draw and how much juice is getting to the batteries?

Any suggestions what/where I should look?

This tractor never has shown that it is charging very well but yet it has never failed to start.

The 8 HID lights are awesome, just don't want to burn up the alt.