Your trim button works fine—until it doesn't. You press UP and nothing happens. Or it goes one direction but not the other. Before you pull the motor off the bracket, check the relay. Trim relays are cheap and fail all the time, especially in salt environments.
This guide walks through how to test a tilt trim relay with a multimeter, what numbers to expect, and how to swap it out when it's bad.
Table of Contents
- What You'll Need
- How the Trim Relay Works
- Step-by-Step: Testing the Trim Relay
- Resistance and Voltage Specs
- Model Differences: Yamaha, Mercury, and Others
- How to Replace the Trim Relay
- Pro Tips
- Common Mistakes to Avoid
- FAQ
- Bottom Line
What You'll Need
- Digital multimeter (DMM)
- 12V test light or jumper wires
- Basic hand tools (screwdrivers, pliers, 10mm socket)
- Dielectric grease
- Replacement relay (match OEM specs or use a quality aftermarket unit)
You won't need anything fancy. A $20 multimeter handles all these tests.
How the Trim Relay Works
The trim/tilt system uses two relays—one for UP, one for DOWN. Each relay is essentially a remote-controlled switch.
When you press the trim button: 1. Low-amperage signal travels from the switch to the relay coil 2. The coil energizes and pulls the internal switch closed 3. High-amperage current flows from the battery, through the relay, to the trim motor 4. Motor runs in the correct direction
Because the trim motor draws 20–40 amps depending on load, you need a relay to handle that current. The trim switch itself only carries a few milliamps.
If one relay fails, you'll typically lose one direction. Both relays dead means nothing works at all.
Step-by-Step: Testing the Trim Relay
Step 1: Find the Relay Pack
The relay pack is usually mounted on the trim/tilt motor assembly or nearby on the engine bracket. It'll have a cluster of wires going into a rectangular block—typically two larger wires for the motor and battery, and two smaller signal wires.
On most outboards, it looks like two relays side by side in a housing, or a single pack with both relays inside.
Step 2: Identify the Relay Terminals
A standard automotive-style relay has four or five terminals:
- Terminal 85 and 86 — coil terminals (low-current signal)
- Terminal 30 — common (battery power in)
- Terminal 87 — normally open (output to motor)
- Terminal 87a — normally closed (not always present)
Marine trim relays often use the same layout but with different terminal markings. Trace the wires if unmarked: two small-gauge wires are the coil; two large-gauge wires are the load circuit.
Step 3: Bench Test the Coil Resistance
Pull the relay out of the pack. Set your multimeter to resistance (ohms).
Probe the two coil terminals (85 and 86).
Good relay: 50–120 ohms Bad relay: Open circuit (OL), or near zero (shorted coil)
No reading at all means the coil is open—relay is dead.
Step 4: Test the Contact Switching
With the relay still out, set the multimeter to continuity.
At rest (unpowered): - Between terminals 30 and 87: should show open (no continuity) - Between terminals 30 and 87a (if present): should show continuity
With 12V applied to coil terminals: - Connect jumper wires to 12V battery across terminals 85 and 86 - Between 30 and 87: should now show continuity (click should be audible) - If no click and no continuity change: relay internals are stuck or burned
Step 5: Test with the Relay Installed
Sometimes a relay tests fine on the bench but fails under load due to heat or poor connections.
With the relay installed and engine off:
- Set multimeter to DC voltage
- Connect negative probe to a good engine ground
- Press the trim UP button
- Probe the large output wire going to the motor
Should read: 11.5V or higher Low reading (under 10V): High resistance at the relay contacts—replace the relay Zero volts: Signal isn't reaching the relay, or relay isn't switching
Step 6: Check the Signal Side
If the relay isn't clicking:
- Set multimeter to DC voltage
- Probe coil terminal 86 (or the signal input wire)
- Press the trim switch
Should read: Battery voltage (12–14V)
No voltage here means the problem is upstream—trim switch, wiring, or blown fuse. Not the relay.
Resistance and Voltage Specs
Here's a quick reference for what you should see:
| Test | Expected Reading | Bad Reading |
|---|---|---|
| Coil resistance | 50–120 ohms | OL (open) or <5 ohms |
| Contact resistance (closed) | <0.1 ohms | >1 ohm = high resistance |
| Output voltage at motor | 11.5–13.5V | <10V or 0V |
| Signal voltage to coil | 12–14V | <10V or 0V |
| Current draw (trim motor) | 15–40A normal load | >60A = motor binding |
The coil resistance spec varies by brand. Yamaha relays typically run 70–90 ohms. Mercury units are similar at 60–100 ohms. Some Johnson/Evinrude designs use solenoids with 5–15 ohm coils instead of standard relays—don't confuse these.
Model Differences: Yamaha, Mercury, and Others
Yamaha
Most Yamaha outboards from the late 1990s onward use a relay pack mounted directly on the tilt motor bracket. The pack houses two relays and is accessible without removing the engine cowl.
Common failure: the relay case cracks from UV exposure and vibration, letting moisture in. The relay itself may test fine but corrode internally. Yamaha part numbers like 6H1-81950 (relay assy) are commonly needed on older F-series motors.
On Yamaha, check the trim limit switch too. A bad limit switch can prevent the relay from ever receiving its signal.
Mercury/Mariner
Mercury mounts the relay pack higher on the swivel bracket or inside the engine cowl depending on year. Older Mercurys (pre-2000) used separate solenoids—big cylindrical units with 5–15 ohm coils.
Newer Mercury FourStroke models integrate trim relay control through the PCM. If you're getting no signal voltage to the relay coil, you may have a PCM fault code before blaming the relay itself.
Mercury's SmartCraft diagnostic port makes this easier to check if you have the software.
Johnson/Evinrude (OMC)
OMC traditionally used solenoids rather than relays on many models—you'll see two large round canisters instead of a relay pack. These are tested the same way, but coil resistance is lower (5–20 ohms). They also fail more often from vibration than from electrical faults.
On FICHT and E-TEC models, the trim system is more integrated. Relay testing is similar, but fault codes should be checked first.
Suzuki and Honda
Both use relay packs similar in design to Yamaha. Suzuki DF-series motors mount the relay near the tilt motor. Honda BF-series often puts it in a separate wiring harness junction under the cowl.
Honda relays occasionally fail from corroded coil pins inside the relay housing rather than internal coil failure. Check the relay socket contacts too—not just the relay itself.
How to Replace the Trim Relay
Locating and Removing the Old Relay
- Tilt motor to a comfortable working position
- Disconnect the battery negative terminal
- Photograph the wiring connections before removing anything
- Unplug the relay connector or remove individual spade terminals
- Note how terminals are oriented before pulling the relay out
Some relay packs are potted in epoxy—if you can't get the relay out individually, you'll replace the whole pack.
Choosing a Replacement
OEM relay packs carry a 30–50% markup over what the parts actually cost to manufacture. The relay itself is often a standard automotive relay—same factory, different box.
SeaSierra sources from OEM-supplying factories. Same specs, no markup. Before ordering, verify: - Voltage rating (12V DC) - Coil resistance spec matches your engine - Contact current rating (should be 30A or higher for trim motors) - Physical fit and terminal layout
Check the service and maintenance kits for complete trim system service parts.
Installing the New Relay
- Match terminal orientation exactly to your photos
- Apply dielectric grease to all spade terminals and connector pins
- Reconnect wires in the same order they came off
- Reconnect battery and test both UP and DOWN before buttoning everything up
Pro Tips
Test both relays. Even if only one direction fails, test the other relay too. They usually age at the same rate. Replace both while you're in there.
Check the relay socket, not just the relay. Corrosion on the socket terminals causes the same symptoms as a bad relay. Clean socket terminals with electrical contact cleaner and a small pick before installing a new relay.
Use a test light for quick checks. A $5 test light tells you if voltage is present faster than a multimeter. Probe the motor wire while pressing the button—light on means voltage is getting through.
Label the relays. UP and DOWN relays are often identical parts. Swap them to confirm which one is bad before buying a replacement.
Keep a spare. Relays weigh almost nothing. A spare relay in your boat accessories kit has saved many trips from turning into disasters.
Heat and corrosion kill relays. If your relay pack is in direct sunlight or exposed to spray, add a small cover or relocate it if possible.
Common Mistakes to Avoid
Testing resistance with power on. Always disconnect power before testing resistance. Voltage on the probes while in resistance mode gives you a false reading—and can damage the multimeter.
Assuming the relay is bad without checking fuses first. A blown fuse kills the whole system. 20-30A trim fuse is the first thing to check. Takes 30 seconds.
Forgetting the ground. Bad grounds cause more trim problems than bad relays. The motor needs a clean, direct ground path. A loose or corroded ground wire causes low voltage and weak performance that looks exactly like a relay problem.
Mixing up UP and DOWN relay wires. Swap the motor wires, and your engine goes down when you want it up. Take photos before you disconnect anything.
Not testing after replacement. Always test full range of motion—all the way up and all the way down—before you consider the job done. A wiring error can be hard to find once you've put everything back together.
Replacing the relay when the switch is the problem. If you're getting no signal voltage at the relay coil, the issue is the switch or its wiring, not the relay. Test signal voltage first.
FAQ
Can a relay test good but still be bad?
Yes. Bench testing checks coil resistance and contact continuity, but doesn't reveal problems that only appear under load or heat. If the relay tests fine but symptoms point to it, replace it anyway—they're cheap.
My trim goes up but not down. Is that definitely the relay?
Usually, yes—assuming the switch works in both directions. But also check for a stuck internal check valve in the hydraulic system. If the relay tests good, the hydraulic side may be the culprit.
How long do trim relays last?
In freshwater: 5–10 years or more. Saltwater or high-humidity environments: 2–5 years is common. Boats that sit more than they run tend to have faster relay failure from moisture standing in the contacts.
Can I replace my trim relay with a generic automotive relay?
Sometimes. Match the voltage (12V), coil resistance, and contact current rating. The relay internals don't care what brand it is. The issue is physical fit—marine relay housings are specific to each engine design. A generic relay may work but won't mount cleanly in the pack.
Do I need to bleed the hydraulic system after replacing a relay?
No. The relay is electrical. Replacing it doesn't affect the hydraulic circuit. If the system was low on fluid or you disconnected hydraulic lines, then you'd need to bleed it—but relay replacement alone doesn't require it.
Bottom Line
Trim relay failure is one of the more straightforward electrical repairs on an outboard. The testing sequence is simple: check for signal voltage at the coil, test coil resistance, test contact switching, and measure output voltage under load. Most failures show up quickly with a basic multimeter.
When the relay's bad, replace it—don't rebuild it. They're inexpensive parts and the labor cost of chasing a half-failed relay isn't worth it. Replace both relays if you're already in there, apply dielectric grease to all terminals, and you'll likely not have to think about it again for years.
