The inspiration for Sledge Hammer! that the creator doesn't acknowledge, at least in the commentaries I heard, is Hunter, a then-current cop show. Sledge Hammer! used the same credits font as Hunter, and the same idea of pairing a Dirty Harry-type cop with a hot female partner. Hunter was pretty rancid, but to be honest, I recall it being funnier than Sledge Hammer when it wanted to be (there was a Hunter episode that parodied Murder She Wrote that was pretty funny). Which is the problem with spoof shows; it's not just that the stuff they're spoofing is already unintentionally funny, but that the originals can be intentionally funny. My problem with Get Smart!, for example, always will be that the James Bond movies had better intentional jokes (the old lady with the machine gun in Goldfinger, for instance). And Sledge Hammer! is pretty much the same way.
Mike Reiss, a Sledge Hammer! writer who went on to become a showrunner on The Simpsons, summed up the problem that Sledge had in finding an audience:
We were trying to do kind of a sophisticated like Police Squad show and our fans were all 8-year-olds. We would get fan mail like in crayon and stuff and kids really loved the show and they didn't exactly know it was a comedy.
Edit: I am reliably informed that Alan Spencer, Sledge Hammer's creator and a pioneer of the "smug is better" school of comedy writing, wrote the pilot script in 1979, and therefore the show was not conceived as a spoof of Hunter (the male-female teaming spoofs the Dirty Harry movie The Enforcer, which was ripped off by Hunter). We at Something Old, Nothing New apologize for our un-rigorous fact-checking, not to mention our lack of reverence for one of those annoying sitcom-for-people-who-hate sitcoms.