the fuse for the speedometer keeps blowing. I changed the fuse and the circit breaker in Dec. 6 weeks later the fuse blew again, I replaced it and it last another 2 weeks and blew again. What is causing and what might be the solution?
Something in the circuit is drawing too much power. The circuit needs to be analyzed and any modules on the circuit probed to find the culprit. It could be a bad module or bad wiring. It could even be a bad connector. Electrical issues are notoriously hard to diagnose. Especially today with the large numbers of computer modules and lot and lots of wiring.
Fuses usually supply power to more than one device so the trouble may not have anything to do with the speedometer circuit. A lot of times problems like this are due to chaffed insulation on the wire. You should invest in a factory service manual for the wiring if you are going to work on this yourself. It will pay for itself with this one job. Ebay is a good place to find manuals for a good price.
There are also shops that specialize in automotive electrical systems, in case it isn’t your forte.
My wild guess is that you have a chafed wire causing an intermittent short to ground in the speedo circuit or one related. A specialist shop will have the schematics, wiring diagrams, and expertise to track it down.
Check the wiring harness for the vehicle speed sensor. A frayed wire shorting to ground might be the problem.