that "P1668" code is what makes me think BCU or IDM. Do you have access to Rave? If so, open the workshop manual for D2 and press ctrl-F and search for that code. It will describe your situation almost exactly.

My 99 did this, and it ended up being the ECM or BCU got wet. I replaced them with a pair from a salvage yard for about $75 each, and all is well. I'm not sure if that is the route to take for you though, just because of the weird issue you've got with the indicator on the dash.

 

Thanks for the rave tip, not the easiest thing to navigate at times.
And yeah, it all sounds like the bcu except the odd dash lights.
But them dash signals for the gear do come from the same plug so possible.