Tech Wiki

M25 (not the XP) Engine Harness Warning/Upgrade

Capt. Al, Kindred Spirit #55

C34s built prior to the 1993 model year run the charging wire from the alternator all the way to the control panel, and then back to the battery, resulting in significant voltage loss. In addition, the control panel wiring employed rubber plugs in the harness, and these plugs are highly vulnerable to corrosion in the marine environment. The upgrade kit, available from Seaward Products (www.seawardproducts.com), routes the charging cable from the alternator directly to the battery, and substitutes marine-approved terminal strips in place of the vulnerable rubber plugs. If you have a 1992 or earlier C34, THIS IS A MUST! The original harness is highly susceptible to failure due to melt-down at best and possibly fire.

Please see this important message board topic -- Strange starting/electrical problem WIRING HARNESS FIRE HAZARD: http://c34.org/bbs/index.php/topic,4546.0.html

Here's one way how:

I did not like the terminal strip method of replacing the harness plugs so I completely rewired the engine to panel with # 12 new wire directly from engine to panel with none of the 14 terminal/plug connections. If I ever have to remove the engine, I will undo the wires from that end. The Amp meter was changed to a Volt meter and the Glow plug button now activates a solenoid to the glow plug. No great need for heavy amps to the panel any more.

Procedure for Wiring Harness Rewiring

Materials: 10 foot piece of flexible plastic 3/4 inch wiring conduit (Electrical Warehouse or Home Depot) 6 - 15 foot pieces of different color marine grade #12 wire (if you can not find six colors, then get three colors and shrink tubing to put on ends of second wire of same color) 1 - 15 foot piece of #10 red wire Variety of types of #12 wire ends and two ends for the #10 wire 12v Solenoid if you are making the power to the glow plugs a direct route (if not you must add another #10 wire) Procedure: Remove all tape and wire ties off the original wiring harness. Remove engine control panel in cockpit.

Start with an easy wire, the temp gauge wire. Follow to plug on harness at engine end, cut wire on both sides of this plug or terminal strip. In cockpit pull wire out to make sure you have the right wire. Cut at both sides of this upper harness plug and follow to temp gauge, disconnect off gauge.

Snake the 3/4 inch electrical conduit from the engine compartment up to the control panel, using the same area as the harness wiring. Pick a color wire and slide it up the conduit, Crimp (bad word for some people, SORRY) on a connector on the engine end and attach to heat sensor. Leave slack to neatly tie up in engine compartment. Go to panel end and leave two feet of cable and crimp end on wire and connect to temp gauge. One wire done. Follow this procedure for all the wires, ONE AT A TIME. Use the #10 wire for the power line to the key switch. The Solenoid for the glow plugs (see other upgrades write-up for solenoid installation) can be mounted on the rear of the engine for proper grounding but I chose to mount it on the fiberglass 2 inch lip over the engine and run a ground wire to its base. One side of the solenoid goes to the starter pos cable, use a #8 or larger wire, the other to the first glow plug. The activating terminal goes to the glow plug pushbutton on the panel. Neaten up all the wires with ties and replace panel. Start engine and see if all instruments are working properly.