No back up lights No reverse lights WAS: 94 100CSQA Multi-function Switch?

[SuffolkD at aol.com]

> From: Franco Barber <feb at febsun.cmhnet.org>
> Subject: Re: '94 100CSQA Multi-function Switch?
> 
> On Sat, Mar 12, 2005 at 09:23:06AM -0500, mwvogt at mindspring.com wrote:
> > Friends,
> > All of a sudden...no back-up lights
> F125 Multi-Function Transmission Range switch.
> Mounted on the left side of the autobox BEHIND THE TRANNY MOUNT!
> <<<SNIP>>>
> 
> 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.
>