the brown wire is a voltage reference wire to tell the R/R how much voltage and Amperage is needed to maintain a good battery charge....
Exactly! The requlator tries to bring the brown wire to the set charging voltage. Supposing the set charging voltage is 14V and the regulator sees less at the brown wire, it increases the voltage on the white wire until it sees that 14V on the brown wire. Likewise, if there is more than 14V on the brown wire, the regulator outputs less voltage on the white wire. So the correct wires to measure are the brown and the black/yellow. If all connections are good, you should see the same or more likely a bit higher voltage at the white wire. Remember, we are trying to measure if the regulator works, not the actual battery voltage.
This scheme of controlling the charging voltage has it's pros and cons. On the positive side, it eliminates the voltage drop in the wires and the voltage is correct where the load is (lamps, ignition etc). On the negative side, if you have bad connections and hence a high voltage drop from the battery to the regulator monitoring input, the battery charging voltage may get way too high and the battery is cooked. Depending on where the bad connection is, you may also have the bulbs blow and other damage. In my opinion, due to the cons, this scheme is bad. If there is a monitoring voltage failure, something breaks. The better scheme is for the regulator to measure the output voltage directly (the white wire). In this case the worst that can happen due to poor connections is that your battery does not get charged.
However, if what Bulldog says in this thread is true, I admit being wrong in this case:
Anyway, if you want to see if the battery gets charged, measure directly from the battery poles - and I mean poles, not the connectors screwed to the poles. Then work your way towards the requlator. If neither the regulator brown wire or the white wire show a good charging voltage, then the regulator is bad (assuming a good AC input to the recitifier).