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MG MGB Technical - Dashboard Turn Signal Indicators

The turn signal indicators on the dashboard of my '67 GT started acting funny a couple of weeks ago. They don't flash regularly. They vary between flashing quickly and slowly. I assumed the flasher was going bad and replaced it, but the problem continues. While testing this evening, I noticed that although the dashboard indicators remained lit almost continuously, the turn signal lights at the corners of the car were working correctly. All the wiring seems to be o.k., and all other electrical items are working fine. What could the problem be? Thanks. -G.
Glenn G

If your flasher unit was replaced with the correct type, and the actual indicator lights are as you say, ok, lets discount these. Only leaves the switch and dashboard lights.

There is an earth wire from the switch to body. First check that this is making a good connection. Check also the green/purple, green/blue and green/yellow wires are all tightly connected in their bullet connectors.
Hal Adams

What about the earth (ground) for the warning lights themselves? The bulb holders are plugged into a funny spectacle shaped metal bridge which is then held to the back of the dash with a couple of nuts. So the earth relies on
(A) Good connection between bulb and holder.
(B) Good connection between holder and "spectacle frame".
(C) Good connection between spectacle frame and dash.
(D) Good connection between dash and car body.
Mike Howlett

The early MGBs had a take off from the relay into both dashboard bulbs which then grounded themselves individually through the indicator switch, depending which turn was being made. This type did not rely on the bulb holders being earthed, but needed an earth from the switch itself

Now, there was a change somewhere along the line, I thought in the late sixties, but if the change was earlier - before 67, then, yes, it will be the earth on the bulb holders as there is no earth on the indicator switch.
Hal Adams

67 was the changeover point (138800 roadster, 139823 GT) from the early 3-pin flasher where the dashboard repeaters were illuminated separately to the corners, to the later 2-pin where they are connected to the same circuits as the corners.

With the earlier type it would be possible for them to come on at different times to the corners of the car, if the flasher unit were faulty. It would be possible for *both* types to be off when the corners of the car were on, if there were bad connections to them, in either earth or flashing 12v supply.

The only way the dashboard repeaters could be on with the corners off with the 2-pin flasher is if their wiring had been changed in some way.

With the 3-pin type it's very difficult to see how they could be on continuously when the corners of the car are flashing if it wasn't the flasher unit that was at fault. The only other explanation is that the light-green/purple wire has been detached from the flasher unit and connected to 12v.
PaulH Solihull

I spent another hour messing with the blinkers this evening, and I think they are working o.k. They are blinking fast, almost twice a second, and that doesn't seem to give the dashboard indicators time to fully darken. Also, they are much faster than with the previous flasher, which did get progressively slower as it aged. It was a Buss 550, while the new one is a Lucas from Moss Motors. So chalk it up to operator error, or at least operator expectation. Maybe the Lucas will slow down as it grows older, like the rest of us.

The car's chassis number is 121xxx, and it has the correct three-pin flasher. I converted to negative ground years ago, and that doesn't seem to matter to the flasher. -G.
Glenn G

My '67B still has it's original flasher, but I replaced the turn signal switch some 25 years ago. Occasionally, the dash indicators stay illuminated when the signals are flashing. Turning the signal switch on and off cures it instantly. The chassis number is 136... and the car has also been converted to negative earth. I suspect poor connections, in your turn signal switch, to be the problem. RAY
rjm RAY

Poor connections would tend to keep the light off, rather than on, surely?
PaulH Solihull

I use an electronic flasher relay on both my MGs. Much more consistent blink rate that doesn't alter with voltage variations.
Mike Howlett

Most electrical problems I've seen on the early B's is traced to loose,corroded, or disconnected grounds, slowly casuing failure over time. Vem
vem myers

This thread was discussed between 27/11/2012 and 28/11/2012

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