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Mercury Control Box With Trim Wiring Question

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  • Mercury Control Box With Trim Wiring Question

    I currently have a 1976 Mercury 500 with power trim with a period correct control box with a separate 3 button power trim switch. I just acquired a newer control box with a round 8 pin connector and power trim built in to the handle that I would like to use on this motor.

    Old power trim switch:



    New control box:



    I can get an adapter or the main wiring harness but my issue is with the power trim wiring. If I understand correctly, my old switch uses a solenoid for the up control but it is direct wired for down and therefore uses a much thicker wire for a higher current and the wire for the down control in the new switch is not big enough to handle the current. It appears that a second solenoid can be installed for the down control which then could be able to be wired to the new control. Is this correct? It was suggested to use a certain solenoid that is obsolete but can still be acquired but at a cost of $60.00 to $80.00. Is there anything special about this solenoid or can I use something different (and less expensive)? How would I wire this?

    Lastly, the new control box has a 5 pin connector in the front of the box which I assume must be for a tachometer connection and some other items that are probably not available on my motor. Is there a harness I can purchase to at least hook up a tach?


    Thank you.

  • #2
    Re: Mercury Control Box With Trim Wiring Question

    You need the solinoid for the down side and it is the same as the up Mercury part # 25661T1 or NAPA # 18-5836

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    • #3
      Re: Mercury Control Box With Trim Wiring Question

      Yes the 5-pin socket on the front of the controller is for a tach, temp gauge and trim gauge I think. There are often tach harnesses listed for sale on that auction site at reasonable prices.

      Here are a couple wiring diagrams for your reference. One diagram shows the wiring for a two solenoid trim system, and the other diagram is of the "new" controller you have. Hope you can read the larger image OK. From these, you should be able to figure out how to adapt the two systems.

      Click image for larger version

Name:	trim NEW.jpg
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ID:	7071167Click image for larger version

Name:	trim DBL SOL.jpg
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Size:	39.9 KB
ID:	7071166

      Good luck

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      • #4
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        Re: Mercury Control Box With Trim Wiring Question

        Thanks, that helps. I discovered that the old Mercury solenoid kit contains a mounting bracket and some jumper wires along with all needed hardware to attach it to my old pump and it is not much more than the solenoid alone.

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