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Re: Tranny Switch Locations
The back up light switch is located behind the center differential lock
vacuum servo on the passenger side of the transmission. The servo is covered by
a tin shield and it makes the switch hard to get at it; you'll have to feel
around behind the servo to locate it. I had my 4kq inspected about a month ago
and ran into the same problem. To get at it, I removed the passenger side wheel
and reached inbetween the subframe and body. You might want to take a course in
Yoga before you do this :). You'll need a ratchet, extension and I think a 22mm
socket (I'm not certain - I'm used to VW backup switches which are smaller. I
just remember this one being larger). Once out, I tested for continunity
between the two electrodes on the switch and discovered it still worked --- the
button on the bottom of the switch just wasn't being pushed in far enough. I
was in a bit of pinch because I was having the car inspected the next day (and
it was late) so, I stuck it in my lathe and took a little off the base of it. I
put it back in and it worked fine.
This is a popular part to have go bad on a 4kq. You can test it without
removing the switch by turning your key to the "on" position and touching the
two wires going to the switch together. If fixing/changing the switch doesn't
work though, I'd inspect the wiring harness that comes into the trunk lid on the
driver side (you'll see it going into the lower driver side corner of the trunk
lid). I've seen a number of 4k/80/90 Audi's where some of the wires in this
harness have actually broken because they've flexed so many times (I ran into
this with my 4kq too). If none of the lights on your trunk work, than this is
definetely the cause. The last and most obvious cause could simply be a set of
dirty/cruddy light sockets.
There is another switch a little further back on the center differential on
the passenger side. It's for the center console light which shows your center
differential is locked.
You're right about Bentley --- when I had this problem it drove me nuts
trying to find an illustration of the BU light switch location :).
Good Luck, Zain
Mail me at mailto:email@example.com
Jeff Goldberg wrote:
> Can anyone identify all tranny related switches and their locations. Bentley
> is pretty poor on this. Trying to see when in reverse :-) 86 4KCSQ
> Found a few pairs of wires, and the wrong pair on the switch I think is the
> backup lite switch, but have not succeeded. Mech tells me the tranny is not
> actuating the switch but I am doubtful (hoping he is wrong).
> 86 4KCSQ Daily Driver
> 86 4KS Spare