The tach goes awol, the idle gets rough and abs light comes on.
It happened for the 2nd time today.
So what/where is the electrical circuit that controls both the abs and idle?
I think I may have a bad ground.
90 sdl
Thanks.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

I think you may have hit the nail on the head.

When I see two completely unrelated systems glitch at the same time the fault, usually, results in a bad ground somewhere. It's the main thing they have in common. (pardon the pun)

Check the easiest first: Batt.-Chassis and Chassis-Engine

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Redid those.
Anywhere else?
Is there a separate circuit for the abs/tach?

__________________
82 300D....went to MB heaven
90 350 SDL....excercising con rods

Check the Overvoltage Protection Relay (OVP) and its fuse.

Especially check for corroded contacts, or loose 'stuff' in relay. Does not sound like a 'blown' fuse.

OVP protects both ABS and Electronic Diesel Control modules, if I recall...

Thanks.
I have retightened everything I could find.

__________________
82 300D....went to MB heaven
90 350 SDL....excercising con rods