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MG MGB Technical - Directional flashers stopped working

My flashers stopped working. Hazard lights work and the bulbs light up when the flasher lever on the steering column is turned either right or left but will not flash. The car is a 1980 mgb roadster. There are two small electrical flasher boxes under the dash on the passenger side. I have tried replacing each with a new unit. The new flasher unit does not solve the problem. Help. Thanks, Dave
Dave

Do you have power coming to the directional flasher unit and is the switch still working properly? It sounds like you need to spend some time with an electrical continuity tester and wiring diagram to trace down your problem.
Jared Snider

Dave. I am having exactly the same problem with my daughter's 77B. The turn signals were coming on, solid, and I replaced the flasher unit with a new flasher from Moss. It worked for about a week or so and now, they come on solid again. I have verified that both lights, front and rear, come on when the directional signal is switched to either side. This, to me, indicates a bad flasher unit. If it were a grounding problem, I would think, that one of the lights would not come on. Was your new flasher unit a Moss product? If so, there may have been a bad run of flashers. I will e-mail Paul Hunt, our resident electrical guru, tonight and ask him to post on this subject. Les
Les Bengtson

The problem is amlost certainly a bad connection in the circuit upstream of the flaher unit. Chreck the fuse box particularly. A volt meter on the power line to the flasher unit should show battery voltage when you operate the switch.

The standard 8FL units are sensitive to voltage and will slow to a stop. The later, electronic, units like the 12FL need an earth but otherwise are a straight swap and are not voltage sensitive, have a constant flash rate and do flash at double speed if a bulb goes.

Chris Betson

Jared, Chris, Les, Thanks for the fast response. The problem that Les outlined is exactly my situation. I have only used a light indicator to check the power to the flasher. I do have power but have not used a voltage indicator. I have two flasher boxes side by side under the dash on the passenger side and the power does go to each. From my manual I really cannot tell the use of the two units but one does read "Flasher". I did get the flasher unit from Moss. I will appreciate any additional input from all of you out there and a special thanks to those who have responded. Thanks, Dave
Dave

In answer to Les:

If both sides got the problem at the same time it is almost certainly something common i.e. something in the green - hazard switch - green - turn flasher - light-green/brown - turn switch circuit. The turn signals are very susceptible to voltage drops, and from experience these are most likely to be in the fusebox and/or hazard switch. I could see that a new turn flasher 'fixed' the problem for a while, either because the (or one of the, there could be several) dodgy connections was disturbed while you were changing it, or more likely because the new flasher will 'age' very slightly in the first week or so of use i.e. its newness was simply masking the real problem. However, Hunt's Fifth Law may also be in effect: "Many break-downs occur soon after a car has been worked on; 'new' parts can be faulty when you receive them; 'new' parts will sometimes fail soon after fitting; 'new' parts almost certainly won't last as long as the originals."

With the turn signals on I would record the voltage on the white/brown and green at the fusebox, each side of the hazard switch, each side of the turn flasher and at the turn switch. I would expect to see a little volt-drop across the flasher (although I have never measured it), ideally none anywhere else but with the current being drawn by two flasher bulbs you are bound to get some. Hopefully it will be obvious from your recorded voltages if it is indeed a bad connection somewhere.
Paul Hunt

This thread was discussed between 16/02/2002 and 18/02/2002

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