Wire from the ignition switch energizes the small terminal on the start relay after passing through an interlock switch, wire is red/light blue. it should be the same color all the way back from the relay through the interlock to the ignition switch on the column assembly. Cable from the D/S battery passes to the P/S battery and from there feeds the starter relay and heads to the starter. Starter relay energizes the starter solenoid.
I don't know if any of our old school buses from the USA have gone to Haiti, they certainly have been sent to a lot of other countries. If so, whoever services those will be probably be able to service your truck. In general most of the older long-nose school buses seem to be international IDI V8 powered while the flat-face ones are pushers with Cummins.
I have a Nippon Denso starter and the hot lead mounting is different from the stock unit. It's sold as a "heavy duty" starter for the same motor in applications from Caterpillar etc. Bolt-on replacement. So I'm afraid I can't help you there.
1992 F250 XLT 4x4 Super Cab 7.3 IDI E40D 3.55 ATS 088 4"R.C 360k
1982 MBZ 300SD W126 California model w/Sunroof, no EGR
1997 Audi A8 Quattro 225k Warm/Cold packages