Suzuki 2 Strokes

Only vaguely connected to bikes but - (well it is a bike trailer!)
Re-wiring it.
I have sealed LED light units - tail, brake, indicator. The tiny 4-pin connector has no indication of which is the earth. So how to test?
I assume I need to use the Diode position on the meter? I'll do it by trial and error today, but I'm curious. Any ideas?

Well using the following (below) now I know WHITE is earth I was able to test using a battery:

Left indicator - yellow.
Right indicator - green.
Reverse - black.
Brakes - blue.
Stop lamps - red.
Earth return - white.
Rear lamps: clearance and side markers, brown.