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You are correct in removing the light bulbs to perform your checks. Tracing a short with the bulb in can give some strange results due to the filament resistance.
You should see if the short is in the hot wire, in the bulb assembly it connects to, or possibly in the switch. My guess would be the wire. To isolate the hot wire, completely remove the wire at the fuse and at each bulb assembly.
With the wire completely disconnected at both ends, there should be infinite resistance to ground from either end. Check each end of the wire to ground to make sure you read infinity. If you read zero or some nominal resistance, you have a short or partial short in the insulation.
I hope it is a total short because they are much easier to find. A partial may only show up when the wire is wet.
Personally, I like using an analog meter for tracing shorts better than a digital because you're only interested in zero vs infinity and exact measurement is not necessary. However, a digital will work just fine.
If you detect a ground in the hot wire, start looking for places where the insulation rubs metal and take Warren's advice about cleaning and checking the bulb holder.
If you post what year your car is, I'll take a look at the electrical schematics on this site to see if I can get any other clues to help narrow the search.
Good luck
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