Thanks Ben.  Note to myself: THINK!  I know that stuff.

OK, overs.  87 Wolfsburg, manual, the backup switch with the separate spade
connectors.  Also, I've added a relay so the wire from the switch is only
triggering the relay, power for the lights picked up in the wiring box.
New tests with a jumper wire:
1. Power directly to the feed to the lights, bypassing everything except
wiring from the wiring box to the lights - lights stay on!  (Eliminating
bulbs and wiring at the taillights.)
2. Pull wires from relay and jump feed from switch to feed to lights
(bypassing relay) - lights go out. (Eliminating relay as cause.)
3. Jump from switch to relay, bypassing harness wiring - lights go out.
4. Jump from power source to supply side of switch, eliminating wiring from
dash to switch - lights go out.

I'm just learning electrical, but seems I've eliminated everything except
the switch.  And you say a bad switch can cause these symptoms.  In each
test, I can keep the lights on by backing very smoothly, riding the clutch
-- either backing abruptly or stopping causes the lights to go out.  If a
bad switch can do that, I need a switch.

Thanks much,
gp

On Tue, Oct 29, 2013 at 11:48 PM, Ben <syncro@gmail.com> wrote:

> Gene,
>
> It's important to specify which transmission you have. The automatics have
> their back-up light switches at the shifter console. Whereas, the manual
> trans have their switches at the nose come area. Jostling a loose wire can
> cause such a problem. A defective switch or bulb can similarly give those
> symptoms.
>
>
> BenT
> sent from my electronic leash
>
> > On Oct 29, 2013, at 11:26 PM, Gene P <olgreywoof@GMAIL.COM> wrote:
> >
> > Question: how can motion extinguish the back-up lights?
> > Symptom:
> > 1. engine off (ignition on), gear in reverse - lights work
> > 2. engine on, gear in reverse - lights work
> > 3. begin to back up, within 10 feet (2 or 3 seconds) lights go out
> >
> > I've gone through these variations many times and it does this every
> > time.  Since everything works while my head is in the engine bay, what
> > can I check?
> >
> > Thanks,
> > GeneP
>