Tohatsu rectifier wiring

[mako2000]

I purchased a charging rectifier to fit to my 2003 18hp Tohatsu but I am having problems getting it working. The Alternator (already fitted to engine and does supply AC voltage) has 3 wires, yellow and white which were plugged together and a black which was alone. The rectifier, (aftermarket by the looks of it) has also has yellow, white and black wires (with the black ending in a ring style terminal to be bolted to earth?) and two red wires (to the battery). Ive plugged white to white, yellow to yellow and tried the black to earth on the engine and connected to the other black wire but still no dc volts from the 2 red wires. (tested with mulitmeter and loaded slightly with a globe style testlight. Im hesitatant to connect to a battery yet as both output wires are red I have no idea which is positive and negative.

The shop I purchased from is now closed for the weekend so I cant ring for advice so I am turning to the Fishraider fraternity for any ideas, thanks in advance guys..