Napa sells a switch that will go on the shifter looks like a 2 speed axle switch push pull go to the Jacobs web and down load all the info I have it all in pdf files
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98 12v,2wd twins,3:55,g56 6speed,elec fan clutch,100 hp sticks, 10 plate FF aFC fB,3gsk Valair ats,fluid damper,60#springs,o6 exhaust brake,High Idle,prime loc, 4"exh,piller mount