In addition to electrical short, don't forget that a degraded system (eg. poor connections, corrosion, improper wire size, or a combination of these) can also cause the thermal overload. It may be that these new lights are drawing too much amperage that the prior foglamp types did not.
If it's not too much effort, I would first try swapping in a set of the other foglamps to see if you're still blowing fuses. You don't necessarily need to completely remove/remount the foglamps, simply unplug the current foglamps and plug in a set of the older foglamp type. This will eliminate the new foglamps as the source of the problem (ie. drawing too much amperage across the circuit).
Next, conduct a wiggle test to see if the fuse blows during the test. If you're blowing fuses due to a short, it should show-up immediately. However, lack of results does not eliminate that a short exists.
Finally, check the connections and harnesses for corrosion and fraying. If you've crimped-in new harness sections or leads for the foglamps, you might also measure resistance across the crimps to look for poor crimp-connections. As you go through the harness, clean the connector ends, and apply dielectric grease as you reassemble each connection.
