1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 211Get this manual
POWER TRIM
General Checks
Before troubleshooting the Power Trim electrical system, check the following: 1Check for disconnected wires2Make certain all connections are tight and corrosion free3Check that plug-in connectors are fully engaged4Make certain battery is fully chargedRefer to the preceding Remote Control or Tiller Handle wiring diagram for connection points when troubleshooting the electrical system(Connection points are specified by number
Troubleshooting the Down Circuit
Connect Voltmeter RED lead to Point and black lead to groundDepress the Down trim button