Why is my gauge fuse blowing up and won't stay on. On a Toyota 4 runner 1994?

A fuse is designed to protect an electrical system from too much power. The fuse is blowing because there is too much power going through it. One of the systems that go through that particular fuse line probably has a short.

Just keep in mind, that the gage may not be the problem, but a symptom. Most vehicles share a single fuse for multiple systems. For example the gage could share the same fuse line as the cruise control and if the the cruise control has a short and blows the fuse, you loose your gages too.