Troubleshooting, Testing and Bypassing SPDT Power Trim Tilt Relays for Boats


Introduction: Troubleshooting, Testing and Bypassing SPDT Power Trim Tilt Relays for Boats

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Troubleshooting, Testing and Bypassing SPDT Power Trim Tilt Relays

Does the electric trim and tilt pump motor not move at all? Does the electric trim and tilt pump motor only run in one direction, only up or only down?

Handy tools: voltmeter, 2 wire jumpers, contact cleaner acid

The motor uses a lot of current so the connections must be clean and tight. When using a voltmeter, the mere presence of 12V can be misleading if a wire is barely hanging on, because it will show voltage but wont be able to pass current needed to run the motor. Don't overlook anything. Be sure to check the wiring to the bottom of the relay sockets for corroded and broken wires!

The up and down relays are identical, so switching them back and forth is OK. When switching the relays, see if the problem changes directions.

IMPORTANT: The engine outdrive trim tilt pump motor will work only if BOTH relays are connected. This is because power to the trim-tilt pump motor is in series with BOTH relays. The direction that the pump runs is determined by the direction of the current flow through the relays. This can be confusing to troubleshoot because there are a total of 10 terminals involved. When you activate either relay by pressing the tilt switch up or down, the internal solenoid winding becomes energized (you should hear the relay click) and the series ground contact is broken and toggled over to a 12 volt input (terminal 87 - the thick red wire). (See diagrams)

Wire jumper configuration to completely bypass the relays and make the motor trim UP:
On the UP relay, place a jumper between terminals 87 and 30
On the DOWN relay place a jumper between terminals 87A and 30

Wire jumper configuration to completely bypass the relays and make the motor trim DOWN:
On the up relay place a jumper between terminals 87A and 30
On the down relay play a jumper between terminals 87 and 30

When replacing relays, always replace both at the same time. If you have installed new relays and the trim/tilt pump motor still won't run, there is obviously a problem with the wiring from the sockets at the base of the relays. Remember this: CORROSION between the male relay terminals and the female relay terminal socket is the biggest problem. CORROSION inside the quick disconnect plugs is also highly suspect.

To test the motor itself, bypassing the relays and relay wiring, find the two heavy gauge wires that lead to the trim/tilt pump motor. One should be green and the other blue. You will probably be able to find a quick disconnect plug near where the wires exit the outboard engine cover that you can disconnect. Ground one wire to any metal surface and provide +12 volts from the battery to the other. The motor should run in one direction or the other. Now reverse the wires and the motor should run in the other direction. This will at least tell you if the motor is operating, so that you will have a better idea of what the actual problem might be. You can also pull out a relay (one at a time) and place a temporary wire jumper inside the relay socket across terminal 87 (the +12DC input voltage source) and terminal 30 (the outgoing wire to the trim/tilt pump motor) to make the motor run. It is worth repeating here: The voltage and current flows through BOTH relays, therefore when testing be sure you have a complete circuit.

Several different 12VDC SPDT relay models will work as long as there are 5 terminals.

Mercury Marine Trim Tab Relays:

- Hella 12V 4RD 960 388-01 SPDT relay (cube shaped relay without bracket)
- HL87411 (waterproof relay with bracket)
- Quicksilver 882751A1 (waterproof relay with bracket)
- Zettler AZ973-1C-12DC4 (waterproof relay with bracket)



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14 Discussions

What is the normal impedance of the trim motor?
Can the motor be dis-assembled and repaired?

We have a problem with our trim on our pontoon boat. It goes neither up or down. We have a new relay, have checked the motor (it's good) and a new tilt trim switch. Still nothing. Help!

1 more answer

To clarify..we have a 91 Mercury 60 horse. It has one relay harness.

My lower unit just locked up and got some wiring hot and blew a hole in one of the relay's I replaced both relays but I'm not getting any power to either or no power to fuse beside relays fuse tested good

I have a Mercury outboard that after I washed it all the sudden the motor started tilting up and would not stop and I had to undo the battery to stop it. And I could touch the terminal with the lead wire while holding the tilt switch in the down position and the motor tilted down. Is this the relay doing this or the switch?

1 reply

I have that same problem can you tell me what it is?

Excellent instructions. Replaced the trim up relay, all is working again. Only wish is that the replacement part was American made. Mercury uses to many made in China and Mexico parts.

This is an excellent "Instruction". It helped me to avoid a $400 motor replacement. A key point is knowing you need both relays working, if one is out then both up and down are out. Thanks!

Also worth noting that the relays can be found at a cost range of $8.00 to $65 each, with no apparent difference other than the housing.


what will cause the relay on the down tilt keep burning out

Great instructions Thanks

Exactly the information I needed, so both relays play a part like the upstairs downstairs light switch.

I gave the opposite relay to the one that clicked a belt with the back of a screwdriver and it started working, however I think I will replace the relay anyway.