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Pre-alpha 1 trim pump change

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klc58

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I have a '73 Searay with an 888 MerCruiser. The power trim pump sounded "different" last year and this year it went down when I put it in the water but wouldn't come up. Since the solenoid operated when I pressed the "up" button (click), I am assuming the motor and/or pump is shot. On top of that, while troubleshooting, I destroyed the switch on the reverse lock valve (which is "obsolete"). The original is a single solenoid system with a reverse lock valve on the shift rack in the back of the motor and the position sensor is piston affair inside the transom. Both are plumbed to the "down" side of the system with low pressure lines (the high pressure "down" line runs from the outdrive into the reverse lock valve).

Since I assumed the pump is bad, plus the unreplaceable reverse lock switch is broke, I purchase Sierra Marine (18-6768) equivalent to the latest MerCruiser part listed on multiple marine part websites. The new pump is a 2 solenoid system. I've disconnected the reverse lock valve and plumbed the "down" high pressure hose to the "DN" port in the pump. The original high-pressure line is in the "up" pump port. (Ok, I know I should replace the lines, but would like to get the pump functioning and see what happens. Trying to get the manifold off the outside of the outdrive is something I'd rather not tackle at the moment!)

I mounted everything and connected the plug. I have power and good ground, but the pump does nothing. I tried to jump the solenoids, but can not get the pump to react at all.

I suspect the problem has to do with the trim position sensor (plumbing is disconnected, the wiring is not). The position gauge pegs high whenever the ignition is on.

I don't care if the position sensor (or gauge) ever works. I'd be happy if the motor went "up" when I push the center button and "down" when I push the lower button (the upper "out" button has never worked since the boat was acquired in '75). I have no problem operating the trim by ear and rpm alone.

But first, I would like to l be able to engage the motor/pump to make sure it works and to get the unit up so I can move it safely!

Any advice, directions, or wiring schematics (even marked with changes) would be greatly appreciated!
 
Unplug switch wiring connector and jump solenoids again. There is a 20 amp fuse for newer pumps, have you checked for that?
when jumping solenoids, how are you doing it?
If you apply 12 v to the small wire of either solenoid it should at least click if not make motor work.

Although not the best method, you can jump across the two large terminals which bypasses solenoid and should cause motor to run.

Try that and report back

your original pump system, one solenoid or two?

Three button trim/trailer/down in dash or toggle switch in control handle?
 
I did check the fuse, it was good.

I tried to jump the solenoids as described, but the plug was still in. I'll try it without. It will be a couple of days though, as the boat is not where I live.

The original 1973 888 MerCruiser (302 Ford) had a single solenoid trim pump with a 3-button dash mounted control. It has an external reverse lock valve on the shifting rack at the back of the motor and the position sending unit is a piston operated affair plumbed in series with the reverse lock valve and is located on the transom behind/above the motor. It has always operated with the "down" and center "up" buttons only. The upper "out" button has never worked, and the up button brings the unit all the way up. it has been this way since the family acquired the boat in 1975.

Anything information that would help me get the new pump to run up and down when needed (after I confirm that it runs) would be greatly appreciated (especially since it is installed and likely not returnable).

thank you
 
You are aware that the trim pump assembly has its own +12 and neg wire that attach directly to the battery?
Should be 10 ga Red and 10 ga Black.
This powers the trim system.

Also, the old one solenoid system push button panel has one wire that was High current that was wired directly to the pump motor which now has to connect to one of the two solenoids as a low current terminal (small post on solenoid).

Hope you understand how they both work.....

If you jump either solenoid directly from the battery, it wont matter if the panel wiring is connected or not as ling as the prior mentioned 10 ga wires are also connected to the battery
 
yes, the pump is powered from the same (always hot) red cable and black ground cable the old pump was. I checked and there is voltage across the unit.

Not totally clear how they both work relative to voltages, etc. that is why I was asking for a wiring diagram. I cannot seem to find anything online (too old, I suppose - the boat and maybe me as well). As described, sounds like the new pump would require a new switch (among other things).

I'll verify pump function, then figure out where to go from there.

Thank you for your advice.
 
Change of focus: how do I determine if the original pump is bad or just the motor? (single solenoid, prestolite model I believe)
It looks like I can get motors (upper section) but not the lower, pump section. (I may have jumped to the new pump too quickly, didn't realize the difficulties in the conversion. Terrrible that all the marine parts websites list it as the "replacement" for the original!)

How can I trouble shoot the original better to decide the specific problem? (probably should have done that to begin with)

Any suggestions would be helpful.

thank you
 
The motor is a DC motor..
It has 3 wires,
Black = ground
Blue is motor spinning one direction
Green is motor spinning other direction.

If you connect black to battery neg

Then connect either blue or green (ONLY ONE AT A TIME) to battery +.

Motor should spin.

What the solenoids do is apply battery + to Blue or green motor wires.
 
IF it doesn't run, how do we know it is the motor and not the pump head locked up?

Also, any chance you can find or direct me to a source for the wiring diagram for this pump? I took pics before tearing it out, but missed a couple of important items. (Like where the little blue wire hooks in and were the 2 different grounds connect..
 
Stop asking questions without answering prior questions please.

Disconnect motor wires, 3 of them from where ever you have them connected.

Connect Black wire to battery ground.

Then touch one OR the other wires (blue or green) to battery +.

If the motor spins then you know the motor works. Of it does not then the motor is bad.

The motor can be separated from the pump section. The whole pump assembly needs to be removed from the mounting bracket. Then remove plastic resevoir, then remove screws holding pump body to motor...
 
I am reaponding thru my phone, when i get on my computer I will upload a schematic. Havent used my pc for several days.
 
The following are three images, one is he new style image of the pump assembly, the other two are the schematic for, The new assembly and the single solenoid old assembly.

Best of luck

Trim pump 1.jpg
Trim pump 2.jpg
Old trim single solenoid.jpg
 
NOTE: In image two the schematic,
The manual had a mistake.
F is the trim limit switch.
E is the Down solenoid.
D is the 110 amp fuse. This may or may not be on your assembly so do sweat this at this time.
 
I had disconnected the wires and the pump did not run (in either directlon, nothing, no noise or anything), that is why I asked for clarification on how we know which is bad: motor or pump head. Of the images provided, mine is closest to the last one. No plastic tank. All metal. High pressure hose runs out the bottom on one side and the low pressure hose (from the reverse lock, position sensor loop series loop) on the other.

Some things that are "different" with mine:
There does not seem to be a tie in with position sensor and the pump. It has always continued to pump (in both directions) when the cylinder limits are reached. We stop when the tone changes.
The switch from the reverse lock valve runs from one side of the solenoid to the switch, then back to the terminal strip. (I have a good image of this "before")

Now for the tear down and shopping for parts...

Thank you for your help.
 
Any suggestions where to find a replacement motor?
I found one from DBElectric that is for "pre-alpha 1 mercruiser" and the picture looks the same, but their support says their documentation does not cover my model.

Found a few used units online but am reluctant to go that route (since the same thing could happen in short order).

Any suggestions of where to look?
Thank you for your help
 
klc58 said:
Any suggestions where to find a replacement motor?
I found one from DBElectric that is for "pre-alpha 1 mercruiser" and the picture looks the same, but their support says their documentation does not cover my model.

Found a few used units online but am reluctant to go that route (since the same thing could happen in short order).

Any suggestions of where to look?
Thank you for your help
Click to expand...
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