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UP and Down Trim not working

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Bitin Bassard

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I have a 1989 40hp merc mariner. Yesterday while loading the boat to leave after a good day on the lake, the trim switch at the control handle and the one on the motor would not work, leaving the od in the down position. Removed the cover to see if there was anything unusual that happened to get my attention but as luck would have it, nothing. Then all a sudden without touching anything, it started to trim up for a split second. It started doing it again so I disconnected the battery cable and it stopped. I was worried if I didn't do that something would of burnt up. The first thing I thought of was a loose connection or a short somewhere. I realize a problem such as that would detail checking the wiring harness from a to z, but hopefully giving the info I gave such as "both switches would not work" maybe you guys can narrow it down a little for me.
 
I checked the control handle trim switch and seems to check out ok. I also by-passed the switches and used jump wires from the battery checking the pump and it worked both directions. Here come the kicker, after connecting everything back together the damn thing started working properly again! I tested both solenoids and they checked out good. The wiring seemed to be tight at the connections. I even wiggled the wires at the motor during operation thinking a loose connection would stop it from operating but no problem there. One thing I did notice, while pressing the up position of the switch on the motor, it was less pronounced than the down position. So maybe I'm thinking the switch is going bad. Just a guess I don't know. The sad part is, it's more than likely going to happen again, of course at the wrong place and time. So I'm throwing another bone out there guys, any takers?
 
I'm glad you brought that up cause it makes a lot of sense! I'll check to see if I can find the part # and order one. I don't have any manuals on this motor either. Would you know if there's a website that sells service manuals for these mercs?
 
I think what Ice and Fazt are suggesting is that the solenoids (electrical relays) are the most likely culprits since they are the ones carrying the main power load for the trim motor, so are the more likely candidates for having burnt/sticking contacts.

The trim switches only have to carry a low current, enough to operate these relays.

If your trim motor bursts into life by itself, that would suggest a 'short circuit' - wires/contacts touching when they shouldn't.

This could be due to a wiring short (any frayed cables anywhere?) which is pretty unlikely in practice and should be pretty obvious if it exists. Or broken trim switches (either control lever or cowl) which are allowing the contacts inside to touch when they shouldn't (again pretty unlikely - usually these switches would simply stop making contact. And again, if these switches are faulty this way, it will usually be pretty obvious; are either of these switches really sloppy and loose in operation, or do they still have a decent 'click' and return firmly to their centre positions?)

(One place where a wiring short could happen, I guess, is inside the control lever, since there is a lot of hidden movement in here. Does the trim motor start up when you move the gear/throttle lever fore and aft?)

And that leaves the relays as possibly being the culprits. There are two of these - one for upski and one downski. Usually they would fail by not making contact when they should (ie - the trim motor won't run), but it's quite possible that the contacts inside are corroded to the point they are stuck and making partial contact when they shouldn't.

I understand the relays are easy to identify and remove. I'm not sure if they can be opened without damage to have a look-see inside?

As for the trim switches, are they 'firm' in operation? If you connect a meter to their terminals, do they make a crisp 'make/break' contacts when operated? When you press them each way and then them release slowly to allow them to return to 'centre', does the meter suggest a 'crisp' disconnecting?

http://************/lib/mercury/manuals/40-50-55-60.html#/86
 
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Just been looking through these threads for help on my own trim switch issue, and it seems that broken wires in the throttle level isn't unheard of. If your trim wires are in the process of being frayed through, they could possibly be touching inside the throttle arm causing your issue.

But obviously that is only a possibility.

I'd have thought that moving the throttle lever slowly backwards and forwards (engine off, but ignition on if that's required for power-trim operation?) would highlight this issue if you are lucky?
 
Thank you very much for your comeback Devs
I'm going to have to agree with you re: solenoids since I'm not an electrical engineer and the fact there's what, 4 or 5 terminals on them and to figure out how to correctly test them is defiantly over my head. Also, like most people, hate to buy without the privileged of knowing if their bad or not I'm going to have to take the exception on this one and purchase them. Of course, making my decision based on everyone's commits about this, which I'm very thankful for!!!
Based on the very little knowledge I have on boat motors, do you know or anyone else know a reliable source where to purchase these relays for a 89 merc 40hp mariner? Preferably on-line since the town I live in is very very limited on boat motor parts.
 
Hi Bitin.

I've been trawling a lot of forums looking for answers to my own 'trim' question, and found many a mention of the relays going faulty. I also recall that they ain't the most expensive of parts (that's nice for a change...) costing around £17 each or something, I think, whereas the actual switches come in at twice that...

Darned if I can find the post that mentioned where to get the relays tho'... Sorry.

Shouldn't be hard to find, tho', I wouldn't have thought.

Re-reading your first post, there are some things one can assume (tho not for definite). Like, if BOTH switches fail to make the trim motor work, then it's a reasonable assumption that it ain't the switches that are at fault. They work independently of each other, so if one fails, the other should still operate.

Obviously what they do then have in common is shared wiring (inside the engine cowl) and a shared relay. So that would suggest the relay as being the most likely candidate for being faulty. But this ain't at all conclusive, of course...!


You suggest you aren't up to sorting this yourself? Fair enough - leccy can be scary stuff :) But perhaps one thing you could try is to pull off the connectors on each relay in turn and see what condition they are in - any corrosion on them?

If you are inspired by this success and want to go further, then you briefly reconnect your battery and try a quick up and down test. (Obviously if your engine is in the fully lowered position, it ain't gonna go down further... ) Note the results. Then swap the two relays around and retry. Report back your findings. (But don't leave the battery connected afterwards. And if it sparks a lot when you connect it up, then perhaps don't proceed any further either...)

The most 'likely' overall candidate is an internal fault in one relay. Or both.

Although the issue you initially had was not being able to raise the engine, this doesn't necessarily mean that it's the 'up' relay that's faulty; it could possibly be the 'down' relay having a partial 'short' inside due to corrosion, and this was acting 'against' the up relay, countering its operation. When your 'up' trim switch then decided to start working, it could have been due to the 'down' relay momentarily going 'good' again!

But - this is all guesswork :)

Let us know what your repair guy finds.
 
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