Spider Fuses redux (Wipers) (Long)

["The Rubies" <rubies@xxxxxxxxxxxxxx>]

Last month I sent a question to the digest about correct fuse values
for a 1975 Spider as my car was blowing a fuse after the wipers
had been operating for a short period of time.

Brian Shorey and John Hewat kindly responded with some sage advice
about double checking the wiring and the earths before tossing
the wiper motor out.  After a month of on-off trouble shooting
(through the heaviest rain Sydney has seen in a few years,
naturally!) here's what I found.  It doesn't make sense unless
you've had a wiper motor apart but here goes anyway.
The Bosch wiper motors have a self parking mechanism that
works by distributing electricity to the motor via a set of conducting
tracks
on the back of a driven gear.  The tracks conduct electricity via some
copper brushes (more like fingers) that can send electricity depending
on where in the "cycle" the wiper motor is currently located.  I'd
never pulled one apart before - they're a very simple but
very clever mechanism.  Anyway, my wipers were toast
from the fuse all the way to the motor:

1) The main power wire for the wipers was actually disconnected.

2) The previous owner had bypassed the "self park" logic of the
wiper motor and wired the wiper switch directly to the motor,
butchering the harness in the process.

3) The wipers were being fed power from the incorrect fuse (number 5
instead of number 2) via a jury rigged wire.

Initially, I re-wired the wiper switch the correct way (not noticing at
this point that the power was coming from the wrong fuse) and
the wipers didn't work at all.  A little trouble shooting with a
multimeter showed that some "extra" earthing was happening
that didn't look great at the wiper motor end.  The fuse blew
almost instantly at this point

Pulling apart the wiper motor, it was obvious that the big fibre
driven gear was intact, but the steam-age electric tracks on the
back were very dirty, burned out and lifting (catching on the
"fingers" and earthing against the case of the wiper motor).

Obviously, the previous "electrician" had realised there was
a shorting problem with the self-parking mechanism and bypassed it
in the crudest way possible.

Down here in Sydney, 105/Spider wiper motors are hard
to come by, but Alfetta motors are easy to find.  Alfetta wiper
motors are identical except they are "reversed"
in their mounting direction - they are designed to fit around the
other way (like a mirror image).  I purchased one anyway to cannibalize
it for the nylon driven gear (complete with good electrical tracks).
After some other fiddling around (re-attaching a burnt out brush)
the original motor now works perfectly.  Actually, it's a very slight
upgrade as the nylon gear is much tougher looking than the
nasty fibre one.

I now have two speeds, no blowing fuses and the wipers self
park.  Of course, the Sun has decided to come out...


dave.

1975 Alfa Spider Veloce "Rusty"
1978 Alfetta GTV "Trusty"
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