How do I wire a 24v starter into a 12 v system?

[NigelBickle]

For all sorts of reasons too boring to go into, my son has obtained a mid 80’s American motor home that hasn’t moved in over 3 years.
All & sundry have been trying to get it to start - as that’s the only way to extract it. We have spend a bit of time, the starter is borked - despite looking fairly new.
So, we now have to jack up this leviathan to remove/ swop out the ( surprisingly small) starter- on this 6.2 diesel. That exercise starts later this week.

Extensive research shows it’s a 24 volt starter, yet the rest of the electrics are 12 or 240 volt.
It did house 2 large truck batteries & a smaller car battery ( I think- half the second tray is missing) presumably to heave the lump over, & leisure.

Now the wiring is a mess, with red & black battery leads going everywhere- making no sense ( to me) whatsoever. Connecting both in series & parallel got us nowhere- wiring direct to the starter got nothing. Not even a click from the solenoid

So, I’ve reluctantly ordered a replacement from Germany, but I don’t want to melt it, as I think he’s happened here. So, I need a wiring diagram that I know works, to follow.

Any of the sparks here knowledgeable in such, please?

[mercrocker]

Nigel, I am not knowledgeable in such matters but I do remember a geezer at work telling me had 24v starter in his otherwise-12v narrow boat. Perhaps some of the boating forums might hold some clues?

[NigelBickle]

Here you go.

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[Hooli]

I'd guess 24v to the main solenoid terminal, batteries also to earth (or maybe the starter casing? check for odd earth straps). Then 12v to the solenoid trigger so the 12v system controls the 24v wiring.

I can't think of any reason not to earth both via the chassis, but I've never touched such a system so maybe wrong.

[Asimo]

The starter solenoid will almost certainly need to see 24v so use a 12v relay to switch 24v to the starter solenoid. You can use either seperate 12v and 24v batteries, or use two 12v batteries in series, taking your 12v from the junction between them.
That should get your starter motoring. Charging is a different problem, check if you have a 12v or 24v alternator.

[panhard65]

Try military vehicle forums as a lot of them were 24v. My old R2087 was but I can't remember how it was wired

[Hooli]

I assume you're going to drive it into the desert & cook meth?

[NigelBickle]

Good idea!
It’s a big empty shell,stripped out by the Owner to trace a leak - then abandoned at my sons place.

Christ it’s big! I don’t even know if We’re licensed to drive this

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Jacking this up, where it sits, is going to be fun!

[Bangernomics]

Aren’t you dead or pretending to be someone else NB?


Less annoying tag line.

[NigelBickle]

Nope. Neither. Sorry