HEllo is there a way to check voltage. or ohms to see if the EHA on a 1989 mercedes 300E is working properly??

The EHA test procedure and specs you want are in the FSM in section 07.3-0121 at page 109. The page exceeds the filesize limit for this website, so I can't post it here, but I can send it to you if you send me a PM.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

I believe it's current draw you're supposed to check on the EHA...

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.