Mercury Power Trim: Diagnosing Electrical Motor Failure

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Author Topic:   Mercury Power Trim: Diagnosing Electrical Motor Failure

casper5659 posted 07-30-2010 10:07 AM ET (US)
I own a 1989 Mercury 115-HP motor. The tilt-trim stopped working while cruising back to the dock. [I] took [the Mercury 115-HP motor] to a boat repair, they disconnected the bullet connectors that run from the tilt motor, and placed the motor contacts on the postive wire from the battery and ground: nothing happened. [The repair man] said the motor was bad. Not wanting to spend $120 labor and $100 for a used trim motor, I replaced [the Mercury trim electric motor] myself by buying a new motor for $150. I unscrewed the lower tilt assembly so that the motor, cylinder, and ram was hanging by the clevis at the top of the cylinder. [I] had no problems replacing [the Mercury trim electric motor]. I refilled the reservoir, and prior to reconnecting the lower tilt assembly back to the boat, I tried [to operate the Mercury trim motor] again: nothing again. I verified 12-volts and 0-volts at the boat-side bullet connectors that attach to the motor connectors in both the up and down position. I can also hear the relays clicking as I actuate the switch. I disconnected both relays but did nothing with the contacts or anything. I just reconnected them. I have placed the motor wire contacts on the positive terminal on my motor block and to ground, and [the Mercury trim electric motor] is doing nothing. Is there anything that I am overlooking? The obvious answer to me--which is not saying much--is that my original motor went bad and the new motor that I installed just happens to be bad, also. What else could be [causing the electric trim motor not to run] that I have not checked? Thanks so much in advance.
hauptjm posted 07-30-2010 10:40 AM ET (US)
First bench test the motor directly. It's a simple reverse polarity motor. Add power directly from a source (battery) to the two leads (pos. & neg.), then reverse the leads and the motor will run in reverse. If you get nothing, then you're correct: the new motor is bad.
Tohsgib posted 07-30-2010 11:36 AM ET (US)
Bench test BOTH motors as well. Always bench test before you assemble because getting a faulty new or rebuilt motor is not uncommon.
jimh posted 07-30-2010 07:02 PM ET (US)
Connect the new replacement motor leads to 12-volts from a known good source of power. This should confirm the motor as either working or not.
When checking voltage with a meter, the current drawn by the meter is very small. If there is any resistance in series with the voltage, the tiny current drawn with the meter will not cause any voltage drop, but, when an actual load, such as a motor for the trim system which could draw 20-amperes, is connected, the series resistance will drop the voltage, possibly to the point where the motor cannot run. Try to check the voltage at the motor in the outboard and when under load.
casper5659 posted 08-02-2010 09:01 AM ET (US)
All is now well. I took the new motor off to send back to the company, and tested it one last time by touching the motor leads to the battery terminals, like I did 100 times while installed. Low and behold, it worked like a charm. I reinstalled it, testing it at various times during the install, and it worked great. I now have a new trim motor, installed for 150.00 vice having a used trim motor installed for 220.00. Thanks for all the help.

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Author	Topic: Mercury Power Trim: Diagnosing Electrical Motor Failure
casper5659	posted 07-30-2010 10:07 AM ET (US) I own a 1989 Mercury 115-HP motor. The tilt-trim stopped working while cruising back to the dock. [I] took [the Mercury 115-HP motor] to a boat repair, they disconnected the bullet connectors that run from the tilt motor, and placed the motor contacts on the postive wire from the battery and ground: nothing happened. [The repair man] said the motor was bad. Not wanting to spend $120 labor and $100 for a used trim motor, I replaced [the Mercury trim electric motor] myself by buying a new motor for $150. I unscrewed the lower tilt assembly so that the motor, cylinder, and ram was hanging by the clevis at the top of the cylinder. [I] had no problems replacing [the Mercury trim electric motor]. I refilled the reservoir, and prior to reconnecting the lower tilt assembly back to the boat, I tried [to operate the Mercury trim motor] again: nothing again. I verified 12-volts and 0-volts at the boat-side bullet connectors that attach to the motor connectors in both the up and down position. I can also hear the relays clicking as I actuate the switch. I disconnected both relays but did nothing with the contacts or anything. I just reconnected them. I have placed the motor wire contacts on the positive terminal on my motor block and to ground, and [the Mercury trim electric motor] is doing nothing. Is there anything that I am overlooking? The obvious answer to me--which is not saying much--is that my original motor went bad and the new motor that I installed just happens to be bad, also. What else could be [causing the electric trim motor not to run] that I have not checked? Thanks so much in advance.
hauptjm	posted 07-30-2010 10:40 AM ET (US) First bench test the motor directly. It's a simple reverse polarity motor. Add power directly from a source (battery) to the two leads (pos. & neg.), then reverse the leads and the motor will run in reverse. If you get nothing, then you're correct: the new motor is bad.
Tohsgib	posted 07-30-2010 11:36 AM ET (US) Bench test BOTH motors as well. Always bench test before you assemble because getting a faulty new or rebuilt motor is not uncommon.
jimh	posted 07-30-2010 07:02 PM ET (US) Connect the new replacement motor leads to 12-volts from a known good source of power. This should confirm the motor as either working or not. When checking voltage with a meter, the current drawn by the meter is very small. If there is any resistance in series with the voltage, the tiny current drawn with the meter will not cause any voltage drop, but, when an actual load, such as a motor for the trim system which could draw 20-amperes, is connected, the series resistance will drop the voltage, possibly to the point where the motor cannot run. Try to check the voltage at the motor in the outboard and when under load.
casper5659	posted 08-02-2010 09:01 AM ET (US) All is now well. I took the new motor off to send back to the company, and tested it one last time by touching the motor leads to the battery terminals, like I did 100 times while installed. Low and behold, it worked like a charm. I reinstalled it, testing it at various times during the install, and it worked great. I now have a new trim motor, installed for 150.00 vice having a used trim motor installed for 220.00. Thanks for all the help.