Moss Motors, Ltd

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.

Umm I don't know a whole lot about the later Bees electrical systems but they are much the same from year to year, so here goes. The hazard switch is connected with the signal switch. If the hazard switch is not working or not hooked up there can't be a complete circuit made for the hazards and signals to work. You could try the easy way as Ive done to rock the hazard switch up&down to get them going again. Most times it works for me. Next would be to check the in-line fuse near the hazard switch.It should be behind the dash on your B and close by. Check and see if it blown, the the last thing I would do is to remove the wires from the switch and use a jumper wire to bypass the hazards to get the signal lights to work. Then at this point you car rule out the signal switch if it works! I would have to look in the haynes book to tell you what wires to jump. I don't know of the top of my head. hope this helps....

hermanmgb

This happened to me once with my '71. After tracing wiring and going over the schematic, I found something interesting. I had used the hazard flashers earlier in the evening. Later, no turn signals. I forget which manual it was, but it suggested the hazard switch be switched off "with vigor" , otherwise "the turn signals may not function". And that's exactly what it was. Hope it's that simple with yours.

In response to your directional signals not working, chances are that it is the hazard switch. I've had many problems after using the hazard lights, all of which are caused by the contacts inside the hazard switch. SNapping on and off several times [firmly!] has always resolved the problem. About your note [#2] the flasher works off the load of 4 bulbs [all 4 corners of the car] and your test light simply won't draw enough current the heat up the flasher and cause it to flash. I hope this helps.

Dan Masters has an easy to read wiring diagram available at http://www.advanceautowire.com  click on stock schematics.  When the hazard switch is on, contacts for the turn signals open and the contacts for the hazards close.  When the hazard switch is in the off position, the contacts for the hazards open and the contacts for the turn signals close.  Hazards and turn signals have different power sources.

Over time the grease in the hazard switch gets hard and the contacts get dirty.  Cleaning the internal contacts in the switch and using new dielectric grease may add years to the life of the switch.

Thank you so much for the advice.  I clicked the hazard switch several times as hard as I could and this fixed the problem.  The directionals now work.  I knew that it had to be something they did when the car got its state inspection.  It must have happened when they clicked the hazard switch.