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Compass Marine How To | all galleries >> Welcome To >> Universal Diesel Wiring Harness Upgrade > What About The Glow Plugs?
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What About The Glow Plugs?

The other high amp circuit on these earlier engines is the glow plug (GP) circuit. While the two cylinder engines can do ok with a 10GA GP circuit, the three and four cylinder engines can suffer from "slow glow" and burned out ignition switches.

A quick and easy way to fix this is to insert a simple solenoid or "pre-heat solenoid" into the glow plug circuit. To install this solenoid you simply steal power via a 10GA or larger wire from the starter post. Please be sure to fuse this run as close to the starter post as possible or within 7".

You then snip the glow plug wire, add ring terminals, and place the glow plug end on the opposite side of the solenoid from the starter wire and the glow plug switch end now goes to the "S" terminal on the solenoid.

Now when you hit the glow plug button a the solenoid (heavy duty switch) closes and creates a direct path between the high current, large gauge, starter motor feed wire and the glow plugs. All the glow plug switch has to do now is energize the solenoids coil, and this takes very little current. You are no longer running high amperage's through 20+ feet of 10GA wire, suspect terminations and switches that are only rated for minimal amperage.

Most all newer Universal, Westerbeke, Beta, Yanmar etc. engines, that utilize glow plugs, have a solenoid in the pre-heat circuit. You can buy one from, called the "Start Assist Relay" and save money.

NOTE: When you do this upgrade we suggest cutting your glow button plug push time to 7-15 seconds maximum. If you hold for the duration that you used to, with the old and dangerous wiring harness, you can literally cook your glow plugs and burn them out.

Glow plugs draw more than most folks assume they do. The typical glow plug off a Westerbeke engine will draw about 22A when cold and as they head up the amperage drops as low as about 11A (test done using constant voltage source and measuring GP current). On a three or four cylinder engine you multiply this load times three or four. Some glow plugs may draw less but most will draw 10A+ each. When you consider that most engines only ship with an ignitions switch capable of 10A or 15A you can see why a glow assist relay can really help.

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HW 09-May-2017 18:14
I am looking at doing this project this weekend. One quick question - do you ground the solenoid? If so, what do you do in order to ground it?