Aboard Astraea

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Preheat Solenoid Replacement


Las weekend when we were anchored in Glorietta Bay the engine was hard to start. When you start our engine first you turn the key on, then an alarm sounds. Next push the preheat button and the alarm turns off, the glow plugs heat up and the fuel pump comes on. In Glorietta the alarm never turned off and the fuel pump didn’t come on. Solenoids are easy to troubleshoot. There’s a 12VDC input at two places, one is the high current input on the left copper post, and the activation is the bottom left small post labeled “S.” When 12VDC is applied to the “S” post it activates the internal mechanism completing the circuit, essentially electrically closing the switch and allowing electricity to flow from the left side to the right.


During troubleshooting I verified that the 12VDc was available on the input. On the output side the large post was 0VDC and the small post was 3.96VDC. I individually disconnected each load on the right side to verify. That they weren’t loading the solenoid down and found the 12VDC never goes all the way through. I looked the part number up in the Westerbeke manual (part number 024639) and found it online for $42 plus shipping and handling. Fortunately, the solenoid is the same as for a 1967 Ford Mustang so I bought it at O’Reilly’s Auto Parts for $24! Thanks to my buddy Vince for knowing that solenoid off the top of his head. I installed the new solenoid last night and it works perfectly now!



  1. Glad you know your friend, Vince! Well worth the “case”!

  2. That same solenoid is in our windlass. But it is such a pain to replace, that the last I vowed never again. I bought a solid state relay to take its place. Bonus: it cost less than the solenoid


  3. Bob, What’s the parts information for the solid state relay? I’m going to get a spare solenoid for cruising, just in case, but solid state technology is way better.

  4. Nate –

    The one I have I bought off of eBay. It is Chinese made, model SSR.YHD2280D. It is capable of switching 80 ams DC, up to 220VDC. Control voltage is the usual 3-32 VDC at a few ma.

    You can find similar ones, in a current rating that makes sense for your application – just search for ‘solid state relay’ on eBay.

    Note: SSR’s can be destroyed by high voltage inductive spikes when interrupting inductive loads (coils, motors). To prevent this, you should always install a diode across the output terminals, or an MOV.


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