Establish which is positive of the rectifier and which is negative.
Using a multimeter on the diode range (or ohms range if there's no diode range)
Put the red meter lead on the negative and test each yellow lead of the rectifier in turn. Then do the same tests with the black meter lead on the negative.
You should have a reading on all 3 in one direction but no reading the other direction.
Now put the black lead on the positive, check all 3 yellows .
Do same with the red lead on the positive.
As before, a reading in one direction but nowt the other direction.
Hope this helps.