Firstly, do you get the red diff lock engaged warning light? If not you will not be able to disable the ABS/TC by activating the diff lock. there is adjustment for the switch that activates the CDL warn light,, mine use to work but now I dont get a warning light when diff lock is engaged and hence my computor is unaware of the CDL on so does not disengage ABS/TC.
If you are desperate to disengage the ABS/TC you can always just pull the fuse as required until you adjust your switch depth.
BARRYJ
I used a flexable drive agencie cable and home made alloy bracket to activate my Cdl, cost about a hundred dollars for a good heavy cable that is sealed against the elements. photos here
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