Merc trim lower unit goes down but not up

[sunk ship]

Need lots of guidance. First off, I have a 1973 Starcraft 18ft SS with a 120 hp Mercruiser I/O. When I got this boat the trim unit was not on it and I later (after a few phone calls, but can no longer find this gent) received the trim unit with a few vague instructions as to how to install it in the boat. He said he had it off to rebuild it... Anyway, I wired it up as best I could and I think I have it wired correctly, but I am by no means sure. Then I put oil in it. Now, when I hit the top button (up) the lower unit goes down. That's right. Down! When I push any other combination of the other two buttons it does nothing. No solenoid indicative clicks, etc. Nothing. Do I need to bleed it? Do I have the hydrolic lines reversed? I have the plastic looking line screwed into the receptacle closest to the front of the boat side of the trim unit. I have the braided looking line screwed into the receptacle on the bottom of the unit. Seriously confused. Thanks in advance for any help you could throw my way.

 

[o-jay]

Re: Merc trim lower unit goes down but not up

I'm no expert either, but I have some opinions...and a real expert will undoubtedly chime in soon.

If you're not sure about the wiring, I would search the web - a wiring diagram is out here somewhere. Generally on these things, your switches just reverse the polarity going to the pump motor - which makes the motor run 'forward' and 'backward' to raise and lower the outdrive. It sounds to me like you've got a wiring foul-up. When you hit the up switch, the motor is turning in the direction that lowers the outdrive rather than raising it. I say this mainly because you said when you try to raise it you get nothing - no click, motor, nothing, which indicates the circuit you're closing has no potential (electricity).

The other possibility is that you've got the pressure/return hydraulic lines reversed, but I would expect the whole thing to work competely backwards in that case, not just one direction.

My vote is verify the wiring first, get the pump to run when you press the switch both directions, then if it's backwards you can move on to whether the motor is running the right direction, the hydraulic lines are right, etc.

 

[Bondo]

Re: Merc trim lower unit goes down but not up

I have a 1973 Starcraft 18ft SS with a 120 hp Mercruiser I/O.

Ayuh,...
So go up to the Adults Only section of this forum,+ download the factory service Manual for your drive...
The Answers you need are in There....

 

[sunk ship]

Re: Merc trim lower unit goes down but not up

I don't think it's there any longer. I have been trying but it sends me straight to a Mercury dealer site.

 

[Don S]

Re: Merc trim lower unit goes down but not up

You are using an old link, go up to the Adults only and look at it again.

 

[sunk ship]

Re: Merc trim lower unit goes down but not up

I think I have figured out most of my problems. Trim buttons mounted upside down. Duh! Ground wire hooked to part of solenoid for no apparent reason that should have had the blue or purple wires from control buttons to raise the unit. Also never could find where these came out of the wiring harness by the engine. Ended up running my own new wires back from the control buttons and cutting existing wires at switch (blue and purple) off because I couldn't find them, therefore who knows where they ended up or what they might be hooked up to and what would happen if they suddenly had power to them. Now since the wire only goes to the middle button I can raise unit or lower at will but since limit switch is wired out of circuit I will have to be careful not to go up too far for whatever reason, because I'm sure that limit switch was there for a reason. Thank all of you for all of your help.

Ps- All I have left is to somehow make the trim unit stop leakin out of the buttom of the reservoir (the seam of the square plate at the bottom of the pump).
)

 

[dubs283]

Re: Merc trim lower unit goes down but not up

mercruiser service manual #1 or #2 is what you need.

unfortunately the trim limit/sender parts for the system you have are NLA

there are wiring diagrams in the manuals that are correct, but since the parts you need are NLA, yes, you will need to cut and splice for the trim pump assy to work. it will work, but not as factory specified.

it sounds as though you are on the right track, and have a good understanding to how electrical systems work.

keep on it, and thanks for the update, it is great when people let others know they fixed their problem