Sierra 18-5953-1 Alternator Conversion Kit for MerCruiser 3.7LX – Upgrade Guide
If you own a MerCruiser 3.7LX (470/485), the original stator charging system is expensive to replace and weak at idle. The Sierra 18-5953-1 Alternator Conversion Kit is the reliable, future-proof fix.
YES – this kit is the recommended upgrade for your MerCruiser 3.7LX.
Why upgrade?
- YES – more reliable: replaces the aging stator/rectifier with a proven belt-driven marine alternator.
- YES – stronger charging at idle: keeps batteries and electronics happier.
- YES – cheaper long term: eliminates costly flywheel alternator assemblies.
- YES – easy to service: standard alternator and belt available anywhere.
What’s in the 18-5953-1 kit
- 68 A ignition-protected marine alternator (Delco-style)
- Heavy-duty mounting bracket & adjuster arm
- Correct V-belt
- Wiring harness & hardware
- Full fitting instructions
Clearance: allow ~100 mm (4") in front of the crank pulley.
Compatibility
- Engines: MerCruiser 3.7L inline-4 (470, 485, 3.7LX)
- Drives: Alpha One / Bravo – OK
- Cooling: Open or closed – OK
- Space: ≥ 4" forward clearance – OK
YES – compatible with all 3.7LX variants.
Tools & materials
- Socket/spanner set, torque wrench, straightedge
- Belt tension gauge (or 10–12 mm deflection by thumb)
- Tinned marine cable: 6 AWG (16 mm²) for B+; 6–8 AWG ground
- Heat-shrink ring lugs, crimper, cable ties, loom
- 80–100 A main charging fuse near battery
- Threadlocker, anti-seize, corrosion spray
Installation – step by step
- Isolate power: battery switch OFF; disconnect negatives.
- Retire old charging: unplug stator leads; bypass/remove rectifier/regulator; insulate unused connectors.
- Fit bracketry: mount the main bracket & adjuster; use threadlocker.
- Mount alternator: align pulleys with a straightedge; snug pivot bolt.
- Install belt: tension to ~10–12 mm deflection; tighten adjuster then pivot; re-check alignment.
- Wire it: B+ to starter battery post or bus via 80–100 A fuse (6 AWG tinned). Ground case to block (6–8 AWG).
- Test: start engine; verify 13.8–14.6 V at the battery; re-check belt after first run-in.
Post-install tips
- Re-check belt tension after the first hour, then periodically.
- Carry a spare belt and fuse on board.
- Low volts? Check belt tension, alignment, cable size, ground continuity, and fuse.
FAQs
Do I need to remove the flywheel alternator?
No. Just isolate its wiring; the belt-driven alternator takes over charging.
Will my tachometer still work?
Yes. The 3.7LX tach reads ignition pulses, not alternator frequency.
Is the alternator ignition-protected?
Yes. The Sierra alternator is USCG/SAE J1171 compliant.
What cable size and fuse should I use?
Use 6 AWG (≈16 mm²) tinned marine cable and an 80–100 A fuse near the battery.
