Solenoid R&R


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Removal and Replacement of Solenoid (preheat relay)

Boat: Pacific Dragon II
Make/Model: 2002 Performance Cruising Gemini 105mc
Engine: Westerbeke 30B - 27hp Diesel
Solenoid Model:  24639

No preheat makes the engine hard to start
The preheat (glow plugs) on the diesel were not engaging properly with was readily apparent from the buzzer that was not shut off when the preheat button was pressed.  By pressing it several times in quick succession it would sometimes engage.  Without the preheat the engine still starts but takes a lot of cranking; too much for my liking. 

Switch or Relay?
From looking at the diagram there seemed only two possibilities, either the switch or the relay.  I picked up a new pushbutton switch at West Marine and had it installed in less than an hour but the problem persisted. 

I then order a new solenoid (preheat relay) from for around $25 dollars and then proceeded to install it.

Here is a picture of the original relay that had failed.  

(Click on Picture to see larger image.)

How to do it without dropping the spacers?
First I marked the wires with different color wire ties and drew a diagram to make sure I knew where each was attached. I then removed the wires and then the two bolts that hold the relay in place.  This is a bit of a challenge since the two bolts with the washers and spacers tend to want to fall into the engine bilge where no man could reach them.  I manage to get them out by using the following method: first loosen the port bolt so that there are just a couple of turns still holding it in place; next use a socket ratchet with a short extension to fully loosen the starboard bolt keeping the socket in place (to hold the bolt) reach over with your fingers and loosen the final couple turns on the port bolt, holding all the lose parts (tip the relay down to keep the spacers from falling off the bolts) and carefully remove the whole works from the engine compartment.  Just reverse the process to install the new relay.  I did this four times that day: once taking it out; once to install the replacement, a third time to remove the replacement and a fourth time to put the original back - all without dropping any bolts or spacers.

Back on with the Original relay!!
You are probably asking why I put the old one back on?  Well after installing the new relay and turning on the main battery power the fuel pump started running. I really could not figure out what I did wrong and put the old one back on to see if it did the same thing (which would indicate that I somehow mixed up the wires.)  The old one did not have the same problem.  I figured that I needed professional help since I really did not understand how I messed up and did not want to damage anything since I have so little experience with diesel engines. 

Help I need a mechanic?
After searching the net and the yellow pages and failing to find a mechanic that had free time within the next 6 months, I called the broker who had sold me the boat and he recommended a mechanic that he used on other Gemini's when they needed work. Fortunately he said he might be able to slip me in the following week provided it was not raining. Luckily the rain stopped for that day and the mechanic true to his word showed up on time.

Professional Help Arrives
The mechanic demonstrated proficiency in following the wiring diagram and testing the circuits involved and came to the conclusion that the solenoid was the failing component.   He then proceeded to install the new one during which he dropped the two bolts and spacers in question at least three times before getting the new one mounted.  I had explained to him the issue with the fuel pump when I installed it and sure enough the same thing occurred after installing the new solenoid again.   He knowing far more about the engine said not to worry the fuel pump running would not hurt anything and we proceeded to test the new relay which worked properly otherwise.  After thirty minutes of looking at the relay and tracing all the wires we still could not figure out why the new relay triggered the fuel pump to run all the time, since this should only happen when the relay is engaged.

Still does not work?
Finally giving up he removed the new relay and reinstalled the old relay and we both agreed that it must be a bad new relay.   We were trying to set a date for him to try again with new parts and it occurred to me that the new relay must be wired backwards.  I told him about my conclusion and he was skeptical but said it was worth a try.   He once again installed the new relay dropping the bolts three or four more times in the process (he convinced me that a magnetic pickup tools is critical for working on engines and was expert at retrieving the bolts and spacers no matter where they landed.)

Swapping the wires solves the problem
This time we swapped the power in side wires with the relay out wires (swap the large wires on the two sides with each other) and it worked as designed.

Here is a picture of the new relay, which required the main wires on either side to be swapped to work properly.


  (Click on Picture to see larger image.)


It works!!!!!
The new relay worked fine when we tested it that day. However on the next trip I noted that the oil pressure warning buzzer sometimes does not properly buzz after shutting down the engine (with the key still on) which is a indicator that the pressure warning sensor maybe going bad (I learned a lot about the wiring in the three hours with the mechanic.)  Always seems to be something going wrong on the engine largely due to corrosion. 

Why did I have the problem?
We concluded that the solenoid failure was probably due to the fact that water had been dripping directly on it from the hatch above from all the rain we had in 2006.  The mechanic recommended that I make a drip protector for it, which I did out of a plastic mixing board they sell for a couple of dollars at West Marine.  I attached it to the deck above (the lip of the hatch with two bolts) so that it sticks out into the opening providing protection for the solenoid from drips from above.   Also, I installed an active anti-corrosion device called, CounterAct, on the engine to help stop the problems from developing further which is documented on another page in my site.

I will not share with you the cost of this learning experience; but lets just say it was not cheap since it took over 3 hours to resolve, but I have a new confidence in my knowledge of the engines electrical system.  Hopefully, the information I provide here will save the next owner who has a similar problem some money.



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This site was last updated 09/01/03