Forum Discussion

Ivylog's avatar
Ivylog
Explorer III
Apr 24, 2015

BigBoy Solenoid not working

I realized this winter that my BigBoy was not working but not necessary when hooked to shore power. Decided today to fix it as the problem is likely corroded contacts because I could hear it click. Disconnected both battery banks and unhooked from shore power so I would not arc weld something. Took about 30 minutes to get it out and apart. Sure enough the problem was corroded contacts and 10 seconds each against the wire brush on the bench grinder... good as new.

Hardest part was getting the two small control wire studs back into their holes in the Bakelite cap. Be sure to push them out when taking the cap off as they have rubber seals and short small wires that do not need to be pulled on. Total time was about an hour and something that anyone with minimal mechanic skills can fix.

If yours is 10 years old and not used often (boost switch and boondocking) then you might want to add it on your preventive maintenance to do list. Even if they are badly pitted, you can file them back smooth which should make them last another 10 years. You can buy new contacts.


  • Ivylog's avatar
    Ivylog
    Explorer III
    Guess I assumed too much... The BigBoy is the battery boost solenoid used on bigger DPs. It also acts as the isolation between the house and engine batteries. When the engine is running it lets the alternator charge the house batteries too.

    With the contacts corroded I wold not have been able to use the boost switch to help start the engine if it's batteries were weak. Unfortunately many places would just replace it $$$ even though its easy to fix.
  • I don't recognize this device. Is it peculiar to a diesel chassis???