87 Delta 88 FE3 Speedo problem

My speedo stops working whenever it rains or the humidity gets high. It goes straight to 45 mph and sits there even when the car is shut off and wont return to normal functions for two or three days later if there is no rain. The car has had this problem since the day it came off the lot. It has been to five different GM shops and to no avail has the problem has never been solved. The sensor has been changed several times by different shops also the instrument cluster was changed once right after it was purchased. Now that the car is getting up there in age the problem is getting worse it will stay like that for weeks before it returns to normal operation. The odometer continues to work correctly while it is doing this. Other than that the only major problem with it was I replaced the timing chain and gears in it last year at 145,000 miles. Any help would be greatly appreciated.

You have an electrical short probably in the firewall entry of the wires. Check the wires out for casing comming off or being rubbed off by the firewall.

Wow, your car wears a speedo. What size is it? lol

A medium. It looks better that way

You have an electrical short probably in the firewall entry of the wires. Check the wires out for casing comming off or being rubbed off by the firewall.

Thanks, I will check that out tonight when I get off work.