More than likely you have a bulb that is shorted and when you put it in reverse, there is just a straight path to ground and the fuse blows. So, we need to remove both bulbs and check to make sure they are intact.
https://www.2carpros.com/articles/how-to-check-wiring
https://www.2carpros.com/articles/how-to-check-a-car-fuse
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
If they are then we need to start checking wiring for shorts to ground.
I am attaching the wiring diagram so that you can run through this info. Basically, we need to put your meter lead on battery positive and touch the other side to each of these terminals to see if there is a path to ground.
Please let us know what questions you have, and we can go from there. Thanks
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Monday, October 11th, 2021 AT 7:00 AM