When you check 3and 4 you will have continuity in one direction ie positive lead on base neg on lead then when you change and put neg on base and positive on lead you will have a slight bleed on newer diodes should not have complete continuity the number 4 rec is the plugging diode if it goes bad it affects plugging when traveling in forward or reverse and change directions it allows the unit to slow down before it goes into direction you also should check your filters they are square blocks with two screws you test them like a capacitor which you need to test as well