I have a 1998 Toyota RAV4 (FWD, automatic transmission). The speedometer sometimes works, sometimes doesn't, seemingly journey by journey - one time, it stuck at 0 at the start of a journey then began working perfectly after about 5 minutes on the road, but other times it either works from start to finish of a journey, or doesn't work at all.
My question is similar to Intermittently fluctuating/non-functioning speedometer in Volvo 940. Possible causes?, but I've never had the needle "wobble around", and my problem seems to be per journey rather than speed related (and obviously it's a different vehicle).
A garage has checked it over, fixed some rusty wiring, sorted out some other electrical issues with the headlights and changed some fuses, and after this it works more often than it did, but it still often fails.
I'm interested in what could cause this kind of "one day it works, one day it doesn't" behaviour, seemingly not affecting anything but the speedometer needle.
I don't think it could be weather related (I'm in West Africa and it's pretty much hot and dry every day, rare tropical rains and no apparent link between rain and the days it does/doesn't work), though I've seen an article suggesting that in some older RAV4s with sunroofs (which mine does have), rain water can leak in and cause problems like this by corroding a connector block (but their problem has different symptoms to mine).
I've read some sources suggesting it might be linked to the transmission - in my case, the automatic transmission seems to work fine regardless of whether the speedometer is having an off day or not. The only thing it seems to affect is the speedometer dial itself.