According to the owner's manual if the hubs are already locked you can shift from 2h to 4h and from 4h to 2h while you're moving. Can't remember the max speed for doing this. And according to the owner's manual you should always stop the vehicle when going to or from 4L.

However, I don't trust the owner's manual on this one. So I have never "shifted on the fly" and never plan to. I always stop.

The wheel lock light is a problem for gen1 monteros/raiders (which is what your 88 is). You can replace a sensor or sometimes the bulb itself to fix that. I had to fix mine but it went out again. No need to worry about the light as long as you can hear it "click" or "pop" when the hubs lock. You can also hear the same sound when it unlocks. Also make sure your wheels are straight when reversing direction to unlock the autohubs.

Welcome.

Roger