[grober]

According to the wiring diagram your 2a fused yellow wire is the constant 12v supply, the red is the 12v supplied via the ignition accessory position and the black is the earth. First check the wires go to the correct position in the plug that plugs into the unit. Then check with the plug disconnected from the unit that you have a 12v constant at yellow 12v switched at red ( ignition switch and warning lights on just before the starter position) and earth continuity on the black. DO NOT USE THE black EARTH wire on the plug for your negative meter contact for the yellow and red tests and use a good body earth to check for earth continuity on the black wire.