Engine speed /dashboard circuitry trouble


#1

1991 Lexus LS 400 with 127k miles on it. Have had trouble with dashboard for a while now, with reverse indicator lighting up everytime I hit the brake.



Just had brake caliper, rotor, pads replaced due to more recent grinding noise.



Now the reverse light stays on all the time on the dashboard! Mechanic said this is not as big a deal as replacing worn brake rotors, pads, etc.



Anyway, now that I’ve had these replaced, my tachometer shows 4 to 5000 rpms even when I;m driving at 30mph within city limits. On the other hand, the engine temp gauge doesn’t show overheating.



Should I be concerned? Or is this just a dashboard circuitry problem I can forestall and safely drive at 70mph on interstate? Incidentally, it was grinding noise and wildly high tachometer reading that caused me to take car to mechanic and have worn brake rotor etc replaced.




#2

The reverse light may be turning on due to a bad ground somewhere. The tach problem may be due to noise on the power buss, perhaps the alternator is having trouble.