Bozair - Welcome to the Forums -
Lots of communal knowledge and experience within the "hive" of the Forum.
The 1986 6.5 McGraw Edison Onan Model 6.5NH-3CR/1600 4P that the '87 345 came equipped with utilizes the 12 volt
windings as the starter.
The "weak link" of the starting system on mine was the "relay modules" -
The 1" black cubes are found on many Ford products - generic units are much cheaper than Onan (Onan doesn't even bother to rename the solenoids) - generic run about 5 bucks apiece - going by memory, but I think there are 4 in the "Control Panel" of the 6.5 KW. The starting system also utilizes a conventional high amp "starting solenoid" (again, when I go into a parts house (NAPA, O'Reilly's, Auto Zone, etc.) I just say it came off of a "Ford").
- Sometimes it's best to just not add confusion to the purchase -
I see from your Public Profile page that you also have a 1988 bronco II.
From that I assume you already are on a first name basis with the manager and all of the counter help at your closest parts store - if not, with the '82 28' you soon will be.
The destination is well worth the journey - during times of tribulation (and there WILL be times of weeping, woe, and gnashing of teeth) you will always find a sympathetic ear here on the Forum.
Remember, there are many ways to accomplish the same mission, and each one of these old MoHos seem to be unique - what may be one way on my unit could well be another way on yours. Factor in 20 plus years of owner "fiddling" and street corner "service station" repairs, and you may well find major deviations of systems from unit to unit.
You might find these links helpful,
Again, welcome, and good 'streamin'.