Thanks! Now revised to stipulate that this troubleshooting applies to SPDT
(not SPST) relays.

Testing, wiring, 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 he 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)