I am going down to my boat tomorrow or Tuesday, so I could take a pic of the relay if needed.
When depressing the pre-heat/cold start button on the generator control panel
, 12V goes to the relay and then to the glow plugs. If the glow plugs are working properly, you can put your finger on them and feel them get real hot, real quickly. If not working, check with multi-meter - black probe to good ground on block and red probe to top of the glow plug
. If no voltage, then work back to relay. Really takes three hands to easily check or use some alligator clips.
Do same check to determine 12V to relay. I will post a pic of the relay. The part was about $30 if I recall
correctly. Probably a third of that if you don't purchase
from Westerbeke. Very simple replacement.
I think that the pre-heat switch also does something else besides the glow plugs. Fuel pump
? In any case I will get back to you.