Odometer won't turn

[cabinetman]

I had purchased a 1988 Chevy ¾ ton pickup that originally had an overdrive transmission I am not sure if it was called a 700R4 at that time or not. The previous owner changed the transmission to a TH350 because he was pulling a lot. The speedometer works fine but the odometer does not turn. Can anyone advise me as to why that may be? I have noticed a white plastic 4 contact pigtail connector hanging loose above the tranny and transfer case. Any help would be much appreciated.