What voltage? Are you running a generator or an alternator? The starter doesn't care what polarity it gets but a DC generator needs to be re-polarized to negative ground. it will probably be necessary to obtain a negative ground voltage regulator, since there are some internal wiring differences. The simplest approach will be to retrofit to a negative ground alternator if possible.

Does the truck have a series-parallel switch for starting on 24 volts? If so, that switch will probably have to be replaced with one for negative ground polarity.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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