Hi Clay,
A 4" hole saw will work. The non light shields have a hole of aproximately 2. 63 inches dia. You can't fit a 4" hole saw thru the bumper. For my '96 I posted the following procedure on another forum. Obviously, if the shields are off the truck then you don't have do go thru all the trouble but maybe some of the steps will help.
My Old Post---
This is the method I used to install the Pilot PL-114C Auxilliary Lighting Kit on my '96 Ram 1500 (in response to a posting on another forum). The reason that I came up with this procedure was to make the 4" holes for the new lights exactly on center of the existing 2-5/8" holes in the plastic sight shield.
I just put in the Pilot 4" driving light kit on my '96 (a while ago). The plastic "had" the 2-5/8" diameter holes where the lights normally mount. I assume your truck is the same. I spoke to a rep at Pilot (emailed and he called right back) and they said the small bullet style lights did not work properly. Very poor performance. I can attest that the 4" lights are very powerful and when properly adjusted will fill in where the stock headlight are lacking. But back to the story.
I was concerned how I would get a 4" hole into the plastic sight shield. You can't just put a 4" hole saw thru the front of the bumper because the opening is only 3-7/8". You can pull off the sight shields but the bumper has to come off and then they are riveted on. Too much work for me. I also did not like the idea of trying to cut a round hole with a razor knife. A hole saw was the only answer to get a perfectly round hole. What I ended up doing required a little set up but was finished cutting the holes in 15 minutes. They are perfectly round and 4" diameter.
The process takes a few steps before the 4" hole is cut. The equipment I used: Reversible drill motor, 4" hole saw, 3-1/2" hole saw, 2-3/4 hole saw, hole saw arbor, circle cutter, a piece of 1/4 rod 12" long.
The reason for the extra steps is that a standard depth hole saw will not cut as deep as the plastic shield extends from the face to the back of the small hole.
1. I made centering guide from 3/4" thick pine board. One circle 3" diameter (circle cutter) and one from the 2-3/4" hole saw. The 2-3/4 hole saw makes a drop out circle that fits snugly into the factory hole. Center the drilled holes of the circles and nail or screw together.
2. Make another centering guide using 3/4 pine board. Use the circle cutter and make a 3-9/16" OD circle. This one is for the second phase and will fit tightly into a 3-1/2 hole.
3. Now that the use of the hole saw with the 1/4 center drill is complete replace the center drill with the 1/4 rod. Grind a flat on the rod the same as the original drill bit. This rod will be used to drive the hole saw from the front of the bumper. The reasons for this are that the center drill will ruin the centring guides and will allow the hole saw to go off center and the drill obviously can't be used from behind the bumper.
4. Assemble the 3-1/2 hole saw.
5. Now the fun begins. Place the centering guide into the small factory hole from behind the bumper.
6. Check the clearnce of the 1/4 rod to the radiator support and adjust if needed. (I think it shoud be about 7" long. ) Cut the 3-1/2" hole from the front of the bumper. Be careful to cut the whole thing at once and not one edge.
7. Install the 4" hole saw onto the arbor.
8. Insert the hole saw assembly into the 3-1/2" hole from behind the bumper. Insert the 3-1/2 centering guide over the shaft and into the hole.
9. With a reversable drill connect to shaft and drive hole saw in reverse while gently pulling and cutting a 4" hole in the plastic. Be careful to cut the whole thing at once and not one edge.
10. Clean up the edges gently with a razor knife and install the new fog lights.
This looks more complicated than it actually was. I had intended to take pictures but it would have taken longer to set up the camera than getting the job done.
For the wiring I decided to use the Pilot supplied harness and switch. The little "mouse" switch is installed on top of the steering column and is unobtrusive.
SteveB
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