Hi: I have a 1988 560SEC, California smog with 170k miles. This morning as I was driving, the radio shut down un-expectedly and the tachometer began to swing to high RPM reading when in fact it was almost idling.
I stopped the car immediately and checked all fuses (including #2 for radio), which were all O.K. Checked the K1 10Amp fuse and also O.K.


Re-started the car and now radio was working again, but the tachometer began to jump wildly upon acceleration. Drove one block and when idling at the street light, the speedometer needle began to show 20 MPH when I was still. Started off the light and the tacho now does not work anymore.


Other than that, the car gave me this morning a few seconds of hesitation when cold (first morning with 56F temperature) so I thought the engine was cold. Once warmed up, it ran O.K.


Any guesses? Is it the K1 going bad? Any other relays? Ignition module going bad?


Your ideas or suggestions will be appreciated.


Nino

Nino. Might be a ground issue up under dash. Many things ground to one post and sometimes that post rots or loses its contact with the body panel (firewall) Look for a mass of brown wires running to one ground.
Clean it up and see that it's stable. Reconnect with some lube.