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Hi. What engine is in your ae100?
Ok thanks. Does the engine rev up like normal?
Generally when the tach is moving slow, it indicates that the tach gauge itself is lazy and needs replacing.
A bad ground would cause various electrical issues. Rust on components would not cause that. Have you checked the charging system voltage?
The charging system should be checked for an overcharge condition. THe alternator can send out RF signals that can be heard through the radio. Also the battery ground and chassis grounds should be checked for tightness and for being clean.
Is what connected to the starter?
No. That tachometer is connected to the ignition module. If the odometer went up also, then there is an instrument cluster problem.
SOunds like you have a problem with the instrument cluster. But you should still check the battery chassis ground.
It is connected to the battery negative cable. Follow the negative cable down to where it mounts to the chassis.
Ok. I think your tachometer may need replacement. But I will opt-out and another expert may have more info on this for you.