I am looking for someone to help me track down an electrical
problem on my 1978 MGB. Following a
state inspection of the car in which everything worked, the directional signals
and emergency flasher stopped working completely (including the dashboard directional
indicator lights). Everything else
electrical on the car works fine. Fuses
are good.
This car has not be overhauled and only has 60,000 miles
with no rust. The wires are in very good
shape and grounding connections appear to be solid.
I thought that it would be easy to track down the failure,
but now I am totally mystified as to how this thing works.
I have a Chilton book which gives the wiring schematic. I located the flasher unit under the glove
box. I thought that, from the wiring diagram, what I should see is the
following: The hot wire is the green one that comes from the emergency flasher
switch. The light green/brown wire goes
from the flasher to the directional switch and then the electricity goes to the
various lights. I tried three testes and
they all failed my expectations. I was
using a standard tester light that has an alligator clip on one end and a probe
on the other end. I removed the two
wires from the flasher unit and ran these tests:
1. I was expecting
the green wire coming into the flasher unit (ignition switch on) to be
hot. It was not.
2. I supplied power
to one pole of the flasher unit and grounded the other side using the test
probe. I was expecting to see the light
on the probe flash. It did not. It was steady on.
3. I supplied power to the green/brown wire going to the
directional switch and turned the direction switch on to the right. I was expecting the right hand direction
lights to light up. They did not.
I pretty much understand how electrical circuits work, but
since all three of these tests failed I have lost confidence in my
understanding of how this
circuit should work.
I need a procedure and series of tests I can perform to isolate the
failure.