Installation Guide – 250A Alternator for Malibu M5/M6/LT4

Tools Needed:

• 13mm, 15mm, and 17mm sockets and wrenches

• Torque wrench

• Belt tensioner tool or breaker bar

• Screwdrivers

• Dielectric grease (optional, for electrical connections)

• Battery terminal wrench

Step-by-Step Instructions:

1. Safety First

   • Disconnect the negative battery terminal to prevent any shorts or electrical accidents.
     

2. Locate the Alternator

   • M5/M6 will be in the upper left. See the below diagram for placement
   • LT4 will be in the lower left. See the below diagram for placement

    

3. Remove Serpentine Belt

   • Use a belt tensioner tool or a 15mm wrench on the tensioner pulley to release tension.
     

4. Disconnect Alternator Wiring

   • Remove the protective cap covering the main output stud.

   • Disconnect the main power cable (usually 10mm or 13mm nut).

   • Unplug the voltage regulator harness from the rear of the alternator.

5. Unbolt the Alternator

   • Remove the upper and lower mounting bolts using a 15mm or 17mm socket.
     

6. Install New 250-Amp Alternator

   • Set the new alternator into the bracket and align bolt holes.

   • Insert and tighten the mounting bolts (torque to ~33-35 ft-lbs or manufacturer specs).

   • Reconnect the power cable and voltage plug.

   • Apply dielectric grease to the terminals if desired for corrosion protection.

7. Reinstall Serpentine Belt

   • Route the belt according to the factory diagram (often on the engine cover or owner's manual).

   • Reapply tension with the tensioner tool and ensure the belt is seated properly on all pulleys.

8. Reconnect Battery and Test

   • Reconnect the negative battery terminal.

   • Start the engine and monitor the voltage at the dash or with a multimeter—it should read between 13.8V and 14.4V at idle.

   • Confirm the alternator is not making an unusual noise and the belt is tracking correctly.

Tips:

• Always double-check torque specs in your engine’s service manual.

• If your boat has a dual battery system, ensure both batteries are fully charged to avoid excessive alternator strain during startup.

• A failing alternator may cause touchscreen flickering, slow ballast pump response, or low voltage warnings.