1987 Chrysler 5th Avenue Oil light on but oil is full

The engine oil light comes on no power to get past 35mph engine gets sluggish and noisy. I checked oil level and its full not over full and clean its been cold out lately and I only usually drive it in the summer. But needed it this winter. I opened the cover to where you put oil in and nothing is wet it looks like oil is not getting in the crank case. I have a manual to do repairs but I want another opinion on this. I think it is the oil pump or somewhere in that area.