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OK, folks, it was a warm day here in Iowa. I drove the '90 740 up on ramps and took a look at how to design an under-bumper bracket for fog lamps. Recall that the curved plastic Volvo bracket works ONLY for pre-90 cars with different air dams.
I wanted to mount the fogs (Hellas) in the cutouts under the bumper. As it happens, these cutouts are directly below the bumper shock mounts, which are bolted into large frame tubes. Luck! The resulting fog brackets are of great simplicity.
On the passenger side, it consists of a drilled 2-1/2 inch by 5 inch stiff plate, mounted with two bolts to the front of the bumper shock frame tube. On the driver side, it is a drilled plate sandwich, bolted on either side of the tow hook with wing nuts. The top side of this sandwich is 2 by 2-3/4 inches, with the front corners rounded off to fit inside the curved tow hook, and the bottom is a rectangular plate 3 by 3 inches. The fogs are mounted in drilled holes in the plates using the normal bolt (not the molly) mounts.
One body mod is needed. To affix the passenger side plate, you need to drill two holes in the frame tubes, superglue two nuts and washers inside the frame tube just beneath the bumper shock, and then bolt the plate onto the bottom of the frame tube. You can also support the plate at the bumper side, but you will have to rivet this as the soft aluminum bumper will probably not hold a thread, and access for a nut is not possible.
I am making passenger-side brackets out of a stiff piece of 3/8 thick ABS plastic: non-corroding and very stiff/strong. The driver's side can be made of thin metal plates, since they are placed on either side of the tow hook and compressed by the wing nuts/bolts.
I'll try to post this idea in drawings when I get time to do them.
My Hellas, which are about 7-1/2 by 3-3/4 inches, will hang directly down from these brackets and fit in the cutouts perfectly. The only negative is that these are only about fifteen inches above the road surface, so illumination won't be as good as if they were on top of the bumper. You will have to be careful about high curbs as well: the usual fog problems.
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