1993 Olds 88 Low coolant light and floorboard rattle

I just got this 1993 Olds 88 with 123,000 miles. The low coolant light is on all the time even though the coolant level is fine. Sensor? If so where is it located?

Second issue is at low speed on gravel or crushed rock you can almost hear a thunk thunk under front drivers floorboard and at high speed it is a lot faster almost like a slight vibration under your feet or like someone is tapping under the floorboard. I am going to put it on a lift shortly and see if a bushing is bad somewhere. Struts and tires seem ok and it drives good but thought maybe someone had same issue and could save me some searching time.

Two other little issues.

Anti lock light on dash on all the time. Any inexpensive way to get that to go out?

It seems like it has some wind noise around the back door drivers side but weatherstripping looks to be pretty good and the drip rail is intact.

Any insight would be appreciated. Thanks

Well I talked with some people and they said maybe sway bar end link or start looking there. I jacked it up and those bushings all seem pretty good.

Well I put it on a lift and checked everything I could possibly find. Ball joint has been replaced on drivers side, but everything looks good. I did notice today that while sitting if I move the steering wheel back and forth I get a little thump so now back to the lift to turn the wheel while it is raised up and see if I notice anything. If the CV joint was going would you notice this at any and all speed or while accelerating or coasting?

Ok here is the latest. I have been driving it, then it rained and then it ran horrible, missing like crazy, barely made it home. Let it sit till warm and dry out and runs like a champ again. Changed the front 3 plugs and wires and running good, then rained and missing again. I need to change the back 3 but any other ideas.

The tire shop said I need struts and ball joints up front.

Mine does the low coolant light deal too.
The sensor is on the passenger side, right below the main rad hose. It's a little electrical plug that should just pop off. Try cleaning the contacts. If it still does it, you can remove the sensor itself (when the car is cold!) and clean/replace it.
Mine only does it when the car is quite cold (below freezing) so it hasn't done it lately, so I just forget about it...