you need axle ratio tire revs per mile do some computations to get total pulse per miles based on the 16 tooth tone wheel in trans and what engine you have electronic or pump line nozzle then using the book at work I look up the dip switch settings temp gauge if its an electronic engine the temp gauge is data link fed and if speedo and tach are working (even if wrong) then the data line is ok and its probably a gauge or dash issue. if a mechanical enngine it could be that or wiring