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  1. O

    1979 Mercury 500 Thunderbolt 50HP losing fuel pressure

    I couldn't agree more. I had multiple issues and thought that I had done everything that I could to solve my fuel problems but it wasn't until I replaced the little 2 inches of hose that connected my carbs together that I solved my issue. My advice would be to change out every fuel line from...
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    1978 Mercury 50HP 2 stroke electric start

    After looking through some wiring diagrams for different motors from this era, some of them use the white wire on the motor side. I think the same harness was used on many different motors and not all wires are used on every motor, like ours.
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    1978 Mercury 50HP 2 stroke electric start

    I have the 1976 version of your motor and have the same wiring diagram. I think the white is tied to the red in the run and start-run positions and becomes the ignition wire to power the choke switch and the tach. It is not needed on the motor side although I don't know why it runs all the way...
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    1977 Mercury 50 HP upper driveshaft seals

    The upper seals are pressed into the end cap of the crankcase. There are no seals on the driveshaft itself that you have to worry about when dropping and reinstalling the lower unit except for the slinger that is pushed over the driveshaft and against the water pump housing.
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    Wiring/Controls help needed.

    Are you talking about the key switch? I don't know if there is a specific switch made for that control box but there are many after market switches that would probably work. You would just have to measure the opening to make sure it fits and that it has the correct terminals for your ignition...
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    Wiring/Controls help needed.

    If your throttle and shift cables still work and you only need new wiring you can get a new harness from CDI, part number 474-9550.
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    1976 Mercury 500 Only Runs For a Few Seconds.

    Hi boaters. My previously running 1976 Merc 500 will not stay running more than a few seconds. If I give it some choke as it's dying, I can keep it running for a little while longer but as soon as don't choke it, it will die. I took it out to the river a few days ago and it ran fairly well...
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    Tach install but confused on engine wiring

    Mercury made a tach specifically for that engine and possibly Airguide also. They are very hard to find and there is not a lot of information about them. I owned that same motor many years ago and could never get a tach to work on it. Good luck.
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