1991 Toyota Corolla Speedometer

I understand in this model, they do not use cables, they use sensors. I have seen the sensor under the hood. Can it be the sensor or the clock that is gradually dying?

Okay, i'll try and check the contacts and clean them if dirty. However, I wanted to test if what i'm feeling is correct or not, what about measuring my vehicle speed with a mobile phone that has a GPS feature, can that work? Would it give me an accurate reading of the vehicle speed?

Right Sir,

Let me try and find a GPS device, and once done, will give you the updates. Yesterday, tried to clean some contacts, I actually followed a cable that enters on the right side of the dash, as mine is a right hand drive, I do not know the functions of that cable, but just cleaned it, and feels like it worked, am not really sure. I tried searching for an electric and sensors diagram for a 1991 ae100 through google, but could not see the link of that cable. I actually want to test it before I make any decisions on replacing any parts for the speedometer, cause here in Tanzania, mechanics are not really reliable, I checked with my mechanic, and he's never come up with such a problem, hence am a little reluctant to give him this job, therefore I wanna make sure myself first before going through any repairs. (My car is my first wife :-)