• If these voltages are not observed, as listed, with a good battery and key switch harness, continue with testing
the power steering signal harness circuit.
• If the voltages are correct across the driver module, the power steering pump may be the problem. Use the
Power Steering Module Primer Kit to confirm a power steering pump failure.
4. Check for proper voltage across the power steering signal harness. To test, break the connection point between the signal
harness and the driver module.
a - Power steering driver module
b - Power steering signal harness ‑ to engine
c - Pin A (black)
d - Pin B (purple)
e - Pin C (white)
NOTE: These procedures cover a single engine application. A multiengine signal harness adapter will be installed on boats
powered by multiple outboards. Be sure to check for voltages listed before and after the multiengine adapter harness.
a. With the key in the off position, no voltage should be present across any wire pair of the three signal harness wires or
across any of these wires to ground.
b. With the key on and the engine off, battery voltage should be present across the purple and black wires.
• There should be less than 1 volt (< 1 volt) between the purple and white wires.
DMT Meter Leads
Red Black Circuit voltage =
Power steering signal harness ‑
key on and engine off
Purple Black Battery voltage
Purple White < 1 volt
c. With the engine running, battery voltage should be present across the purple and white wires as well as across the
purple and black wires.
DMT Meter Leads
Red Black Circuit voltage =
Power steering signal harness ‑
engine starts and runs
Purple Black Battery voltage
Purple White Battery voltage
• If these voltages are not observed, as listed, with a good battery and key switch harness, check for the same
voltages at the engine wire harness which connects to the signal harness. If the listed voltages are still not
present, a problem may exist within the 3‑wire circuit on the engine wire harness or the PCM. With the PCM
disconnected, complete an ohms/continuity check on these wires. If the circuits have no shorts to ground and
less than one ohm of resistance, a PCM may be the problem.
Power Steering Module Primer Kit
If the power steering pump is inoperable, a great way to test the power steering pump directly is to utilize the power steering
primer module to bypass the engine and all boat harnessing. With battery power hooked to the power steering pump and the
primer module installed, a working power steering pump will operate when the two‑stage module is activated in the proper
sequence. See the instruction sheet supplied with the power steering module primer kit.
Power Steering Module Primer Kit
91‑895040K01
Accessories
Page 5C-6 © 2018 Mercury Marine 90-8M0146617 eng JULY 2018
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