I'm hoping someone with a bit more knowledge than me chimes in but they look like what you stated.
Whether you have 2, 3 or even 4 12volt batteries wired in parallel, its still a 12 volt bank of batteries.
The wiring dia. ( I posted earlier) uses 4 6volt batteries two sets of two wired in series effectively giving 2 12 volt batteries.
Your set up of 3 maybe to give more cold cranking amps.??
If your KW is 24volt start 12volt run, ?? there should be a series parallel switch close by the battery box which looks similar to these in attached PDF.
There has been a few discussion here before on Kenworth charging / starting systems, try and search back through the threads if no one else can help.
In order that the labour of centuries past may not be in vain during the centuries to come...Denis Diderot 1752