93 f250.

my tach is intermittent. some times it doesn't work at all, some times it works great, other times it doesn't register anything at an idle, but when i give it gas it seems to work but i'm not sure its accurate.

it seems like a few years ago i had the instrument cluster out to change a light bulb and cleaned the dust out the fach worked great for awhile after that but then it went back to its intermittentedness. there were some contacts on the back of the instrument cluster, i wonder if they're dirty and not gettng good connection? its all electronic.

 

Check the wire/nut connector on the side of the oil Fill neck.

Very common place for them to fail, with age and wear & tear they start showing bear wire and start to act weird.

 

X2^^
Might just be time to replace it.

 

Keep in mind that you don't have to use the OE Ford sensor. You can use a sensor out of a road tractor. Eaton, Rockwell etc. use the same thread on their sensors. They will be adjustable. Screw it in till it touches the gear and back it out a 1/4 turn. Can save you some money. Any truck parts place should have one. Hard wire it in and go. You can also check one of these sensors by moving a metal object like a chisel across the tip of it pretty fast. Chuck something up in a drill like a rear sprocket off of a pedal bike.