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Project: Glow Plugs

This page describes C34 owners' solenoid for glow plugs upgrade project. 
Please contribute yours!

Solenoid for Glow Plugs

The installation of a solenoid to the glow plug circuit will reduce the time to hold the key or push button that powers the glow plugs preheating the engine before starting. Shorter, larger wires = more power to the glow plugs!

Parts list:

Solenoid, 12v, O.E.M. Quality Solenoid  Ford Starter Solenoid SW3 STD # SS581, Niehoff #FF143A or Wells #F-496  approx. $5.00

Six feet of #8 wire

Three large stud round wire connectors (#8)  for starter (1) and solenoid studs (2)

One small stud round wire connectors (#8)  glow plug

Grounding wire, two feet #14 wire with end connectors

Two bolts, nuts and washers


1:  Mount solenoid with its mounting flange  tabs. Most solenoids have two tabs with holes for mounting. These tabs must be grounded for the solenoid to work. Fabricate a plate or find close to matching mounting bolts on the rear of the engine. This was not possible on my M25 so I mounted mine UNDER the fiberglass/wood lip that the engine hatch rests on, above and rear of the engine. This means that it is hanging upside down over the rear of the engine. Two bolts were used to mount it, using one of the bolts to connect the ground wire that is wired to the ground on the engine.

2:  Remove white (I think its white) wire from last glow plug. This is the wire that goes up the wire harness to the glow plug switch. DO NOT cut the end off the wire to make it shorter. If you ever have a problem with the solenoid, then you can connect the system back the way it was. Connect this white wire to the small stud on the solenoid. Some solenoids have two small studs. One is not used. Before installing, ground the solenoid and touch a hot wire to the small studs one at a time. One of them will make the solenoid CLICK. That is the one you connect the white wire to.

3:  Connect the (+) side of the starter to one large stud on the solenoid. Use the #8 wire, cut to size with the end connectors crimped or soldered in place.

4:  Connect the other large stud on the solenoid to the glow plug where the white wire was removed. Use the #8 wire, cut to size with the end connectors crimped or soldered in place, one large and one small connector.

5:  Go to engine panel, turn on key and push the glow plug switch and you should hear a click of the solenoid down by the engine. Hold for 25 sec, shut key off and return to engine and see if you can burn your finger on the top of a glow plug. It still should feel hot. I now hold the push button for only 12 sec instead of 25 to start the engine.

Comments:  The engine panel is fused, so the control of the solenoid is but the (+) from the starter through the solenoid to plugs is not. This is a problem if the solenoid should malfunction and remain HOT. You will burn out your glow plugs because you will not notice they are on. I have never heard of this happening but I have a safety light that I have added for this.

Safety Light:  Purchase a 12v low amp auto, 1/4 inch, dash light that you mount in the engine control panel. Ground one side of the light at the panel and run a #14 or #18 wire down to the top of a glow plug or that side of the solenoid. When you hold the glow plug push switch on, the glow plugs and the dash light will both be on. Release the button and they both go off.
(Capt Al) #55 "Kindred Spirit"

I have a few more ideas to add to Al's procedure.  If you have a M25XP engine, you can mount the solenoid thru the bolts that hold the heat exchanger in place - it saves a lot of work.  As I mentioned in the Aug.97  Mainsheet on this topic, don't cut the old wire.  If the solenoid fails, you can always connect it back to its original wiring. Take a #2 pencil and spiral the wire around it to take up the slack If you want, you can mount a safety light, but you already have a ready made indicator on the engine instrument panel to let you know if the glow plugs are engaged and when they are disengaged -- it's the voltmeter.  When you engage the glow plug switch, the voltmeter will immediately drop about 1+ volts.  When you release the glow plug switch, you will see the voltage go back up.    This should be a good enough check as to whether the solenoid is working or whether it is stuck. I have always found, the majority of the cost is in time doing the work.  As I mentioned in that Mainsheet article, if I had to do mine
over again, I wouldn't skimp and use a Napa Ford starter solenoid for $13.99, I'd use a marine grade West Marine solenoid for $19.95.  The marine grade is probably a more reliable solenoid in the long run.

Here's the wiring diagram that Stu sketched.

Important: The opinions expressed here are those of the individual contributors to this page, and not those of the Catalina 34 National Association or Catalina Yachts, Inc. Additionally, this material has not been reviewed by Catalina Yachts, Inc. for technical accuracy. This page's maintainer cannot guarantee the accuracy of this information or the desirability of suggested modifications or upgrades. Please obtain assistance from a competent marine mechanic or boatyard prior to making any significant modifications to your vessel.

Last modified by Phil Imhof, Wednesday, August 11, 2004 . Copyright 2001 by Catalina 34 International Association.  All rights reserved.