Tacho went out (kinda.) Help?

[joan]

So a little while ago my tach kinda just slowly died out. Engine still runs alright (its got its slight issues, obviously, but the rpm's are always steady.) At first it would either stop completely, and then come back 100% working, but now it does this thing where at low rpms (0-3000 ish), it wont work, but it will start working around 3000+. So like when i rev high ill watch it jump up from 0 to whatever its "working" range is, its quite funny actually lol. Anybody know where the issue could be? The gauge itself, wiring, maybe bad ground? Anything helps, thanks. Also where would I begin looking for the issue/ where to dig in to fix it? I've no idea really how the tachometer really works, so it'd be a great learning experience for me.

 

[Firewout]

Joan, is your cruiser petrol or diesel?
I started a thread for a diesel some years ago.

 

[joan]

Its a petrol. '96 1FZ-FE

 

[Firewout]

Factory service manual is always a good starting point.
Link downloads the electrical wiring diagrams fsm for your cruiser.

https://drive.google.com/file/d/0B23Isi3fiMPOX29SQWFuWWdDaUk/view?usp=drivesdk&resourcekey=0-MziTpx1aMQGeXO020buc4A

Good luck.