How can I train my 8-year-old rescue dog not to pee in his crate?

Didn't the rescue people tell you his history? Is he afraid to go in? Do you shut the door? How long does he have to be in it? Maybe a former owner put him in a crate for punishment or shut him in too long. Do you take him for walks during the day?

Suggestion would be to provide water and feed the pet in the crate. Usually animals will not use the toilet where they eat. Years ago I had to do that with my one Sheltie but she was gated between the kitchen and bedroom and not in a crate. She would go when I walked her but still continued to do her business inside til I put her food where she was gated and that stopped soon after that.