On a 77 and later the horns work by receiving 12v on a purple (fused always
on) on one side of the switch and sending it on a purple/black to the horns.
The horns pick up a ground from their physical fixings. Ironically until
the 77 model year the horn switch *did* use a ground, but it was picked up
from the column itself not a black wire. Collapsible columns can get
problems with these grounds due to their construction, and I have had
problems with a horn button as well.
The wiper switch does not involve a ground after 1967. 12v is received on a
green (fused ignition) and distributed to a red/light-green for the slow
speed, and a blue/light-green for the faster speed. Parking is achieved by
connecting the brown/light-green to the red/light green. The motor has a
green supply for parking, and a black ground for both running and parking.
Not a lot of opportunity for repair, and they are expensive to replace,
especially the single combined stalks on the later cars.
The washer switch *does* receive a ground from a black wire and extend it to
the motor on a light-green/blue, the motor having a green (12v) on its other
terminal.
If the Weber electric choke has its own thermostatic switch like the
Stromberg system then all it probably needs is the green wire that came off
the Stromberg heater connected to the Weber.
Do the parking and head lights work OK? Just not the dash lights? These
take a tapping from the red/green wire from the main lighting switch via a
rheostat to power the instrument lights. The rheostats *are* prone to
failure, every car I have bought with one has been faulty. The main
lighting switches are not generally fault prone unless the headlamps have
been uprated or fog/spot lamps powered from them. These upgrades should
always be done with relays. If the parking or headlights don't work either
then the main lighting switch is probably the cause, bypass it by linking
the brown to the red/green and blue to check. Take care, the brown is
always live and unfused, shorting this to ground will damage the loom and
connectors.
PaulH.
----- Original Message -----
From: <DMatt21502@aol.com>
To: <mgs@autox.team.net>
Sent: Monday, February 28, 2005 4:50 PM
Subject: Ahh, life is good. 77 MGB back on the road.
> ... Neither the horns or the windshield washer or wipers work. ...
> ... Also I have a Weber carb with electric choke.
> ... the dash lights worked fine but last night I noticed they don't come
on anymore.
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