The rectifiers are very expensive ( $174 each mercury and $158 each CDI) and sometimes the stator ( $467 Mercury and $430 CDI) will be the cause for failure. So you may replace both rectifiers only to find in a very short amount of time they will go bad again and you have wasted money. I have converted several 40 amp systems to 9 or 16 amps depending on what engine I was dealing with. With the EFI you would want to go with the 16 amp if you chose to convert. Usually you will find that is is a lot cheaper to convert than to repair the 40 amp system and will have a trouble free system. I have seen it several times. The 40 amp systems will kill rectifiers left and right. It is sometimes from poor connections and will damage the wiring on the stator. But to ensure that you won't have a repeat failure on the 40 amp system, many will suggest replacing both the rectifiers and stator as I do. If the rectifiers fail shortly, the company will not warranty them. Just my experiences.
Usually the speedometer is wood in the hole and is a simple fix. Thing is it will just continue to occur. The water pump is a suggested item that should be replaced once a year according to the service manual. Hope this helps!
