Dakota digital tail light circuit

[elorenzof]

1970 c10 - dakota digital HDX gauges - the instructions say for the module dim(+) connection to hook it to the taillight circuit.

The dim(+) is for the backlights and needles on the cluster to illuminate when the headlights are turned on. What wire should be used? Could I use the grey wire that illuminates the dash lights from the factory wiring that is in the factory plug that goes into the back of the original cluster? (Actually new M&H factory upgrade replacement dash harness) that factory plug also holds the left and right turn signal, high beam, etc wiring for the cluster.

If i can't or shouldnt use that one, where from / how did you get the source for that dim(+) connection?

Any help would be so awesome.thank you so much. ~ Lorenzo