'94 100CSQA Multi-function Switch?

[Franco Barber]

On Sat, Mar 12, 2005 at 09:23:06AM -0500, mwvogt at mindspring.com wrote:
> Friends,
> All of a sudden...no back-up lights. I'm told it could be the multifunction switch on my '94 100CSQ Avant. Never knew these even existed or if any of my other Audi's have them. Told it is mounted on the left side of the autobox. 
> Anybody had any similar experience or could shed some light on this switch and what it's multifunctions are, before I open an electrical pandoras box.

F125 Multi-Function Transmission Range switch.
Mounted on the left side of the autobox BEHIND THE TRANNY MOUNT!
Impossible to get to without removing the transmission mount.
Need to support the engine (from top, according to Bentley, like you
were going to remove it) before removing the mount.
There could be many shortcuts to this, I don't want to speculate.

It's a 5-pole switch. Three of the poles are arranged as a binary signal
and drive module J127 (Transmission Control Module -- among other things,
it shows the selected gear on the instrument cluster.)
One pole drives modules V94 (Central Locking modules) and
J192 (MFI Engine Control Module) and J221 (Shift Lock Control)
but only when the MFTS is in N and P position.
The final pole, active only in R, drives a part of relay J226
(Park/Neutral Position relay) that controls the reverse lights.

Of all these things that it drives, most of them (various modules)
are solid state devices with high impedance inputs.
Only J226 is a relay with low impedance inputs.

So, my theory is that what happens is that as the F125 ages the internal
impedance of the contacts goes up, and eventually the impedance of the
contacts when closed rises to the point that the voltage drop across the
switch in the closed position is high enough that there
isn't enough voltage left to activate the J226 relay.



Franco

-- 
Franco Barber                   feb at febsun.cmhnet.org
95 A6Q w/Gamma CD mit RDS!      Columbus, Ohio  USA
95 A6Q 5spd w/HCB-30 bluetooth car kit!