In my 87 BII, the #6 fuse for 4wheel drive indicator (and a few other things), is next to #5 fuse for turn signal and backup lamps. There could be a crossed or bare wire in this area, or in the harness nearby.... Might check. Where I am, we have some crazy little woodland rats that like to climb into our vehicles and chew wires.
I would start at the 4x4 wireing and trace back to fuse, since you know when you shift into 4x4 (the indicator light should come on via the 4x4 indicator switch) you end up blowing the fuse for turn signals. It stands to reason that if you open the circuit by removing the 4x4 indicator light, it should temporarily solve the problem. (I would do that myself just to see if it does).
If this proves to be the case, you are relatively sure it is on this circuit. THEN (still) you need to trace that circuit and find the short.
Could be wrong, but that is where I would start.
