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RE: weird ABS light flicker

Hmmm. Well, the differential lock disables ABS.  I *believe* the differential
lock light is actuated by an electrical switch right on the differential.  This
means the light is an actual indication of the state of the the differential
lock (as opposed to the state of the dash switch). If for some reason, the
differential tries to lock, the light will come on and simultaneously turn off
the ABS.  This could be as simple as a loose vacuum hose to the differential or
as bad as a dead servo on the differential.  I bet the ABS system is just fine. 
When ABS turns on, it goes through a self test which runs a fairly heavy duty
electric pump in the hydraulic modulator.  This may account for the big voltage
surge you see.

My guesses,
Maynard, MA

>I have a weird problem of sorts that leaves me scratching my head.
>The car in question is an 89 200q.  When the car accelerates rapidly
>(ie. passing trucks going uphill on the highway at say 65~70 mph
>sorry no metric, I'm in a rush ) the abs light blinks on for a second
>or two or three then goes off with no assist from me (I don't touch the 
>ABS switch) at the same time the wife tells me the green light from the 
>differential lock switch blinks on and the voltage gauge flickers 
>+/-3 V (this is noticeable as my headlights flicker) when the light goes off.
>Neat huh.  Well I can feel my charge card getting warmer as I think 
>about what could be wrong.
>So, anybody feel challenged by this kind of bug?  I'm all ears,  and would 
>love to know what to check first.
>thanks in advance
>jim h 

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