Mercury v6 200 efi bias wire removal joining switch boxs enexpected result?

Chasing a high speed miss and intermittant low speed one side dropping out. Motor first had a bad switch box at low rpm ( both were exchanged). Detonation and idle control boxes are removed only oil tank module left. Grey white wire is grounded. Now motor has spark on both sides at low rpm but one side loses spark when going to the higher rpm. Have swapped out (40 amp )stator, tried disconnecting the regulator wires with no effect but when I remove the bias wire between the boxes both sides have spark again. What am I missing maybe one of the replacement boxes is wonky?

Sounds like your stator and or regulators took out your first switch boxes, and then your second switch boxes. There is no way to test switch boxes but you can do a quick ohm test on the stator just to be sure. If that tests out ok make sure all your grounds are in good order. Add some more they can’t hurt. If that doesn’t flag anything then I think I’d maybe look at the switch boxes again. There’s probably more to check but that’s all I can think of today. Fried

If you dont have a dva? Swap the red and blue wires from one sb to the other. If your miss moves to the other side of the engine it's a bad stator. You can also unhook your bias wire and test resistance on each bias lug, they should be close to the same resistance.

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Originally Posted by OnPad

If you dont have a dva? Swap the red and blue wires from one sb to the other. If your miss moves to the other side of the engine it's a bad stator. You can also unhook your bias wire and test resistance on each bias lug, they should be close to the same resistance.

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This is right on the money. Do this ^
Check bias resistance to ground. If its way off on one box change em both again.

The DVA readings are good, so I did the "bias test". I have a few boxes so did them and what I am seeing is some are in range(13--15,000 ohms) but a couple would flash a resistance in that range then drop to zero (so NFG). This was good to see. Thx all for replies