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MG MGB Technical - One side indicator running slowly or staying on

So here we go.... My 1973 MGB has an "issue" with the indicators. The left hand ones flash as normal, but the right hand ones flash either very slowly or come on and stay on, with no flashing. The hazards work fine - both sides flash.

So, should I be looking at the flasher unit (but then why does it flash for left but slowly or not at all for right), or somewhere else ?

I've cleaned up the connections in the actual light units on the RHS today, but this has made little or no difference.

Help ?

Thanks
Andy
Andy Smith

Andy,

it was the same on my V8 two years ago. Due to the layout of the flasher unit, it must be a mistake anywhere else. On my car i used contact cleaning spray for electronic switches (not the stuff sold for cars) on the switch in the steering colume. It worked and the problem was gone!
I do not know wheter there are other 'typical' faults to search for, but if you have a look at the wiring diagram, it is most probablle that a bad connection there will cause the difference.

Hope this helps

Ralph
Ralph

Andy - the first thing to check is if either the front or rear bulb is different - swap them, on at a time with th bulb from the other side. If the problem goes to the other side, you have a bulb that has become flaky or is the wrong bulb (I have had that happen. If this doesn't cure the problem, start by cleaning the switch as Ralph suggests and the work your way out to the front and rear lights, cleaning each bullet connector (both the bullets and the sleeves), ending with the light sockets, cleaning the inside of them. Move to the ground connections - the mounting screws for the front sockets and the ground wire and it's grounding point for the rear sockets. See the article, Ground Wire Preparation in the Other Tech Articles on my web site at: http://homepages.donobi.net/sufuelpumps/ If this doesn't cure the problem, you may have a corroded crimp in one of the bullet ends at one of the bullet connectors. The easiest way to find if this is the case, is to use a long piece of wire and jumper from the switch to the socket. Whichever leg cures the problem is where the problem is and you will have to work through all the connectors in that leg to find the bad crimp (I found a situation like this in our daughter's MGB GT. Cheers - Dave
David DuBois

As the problem is sided it must be between the switch and the corners of the car on the affected side, as you rightly surmise a problem wwith the flasher unit would affect both sides equally.

The two flashers are deliberately designed differently. The hazard flasher has to be able to flash anything from one bulb to four bulbs and for long periods i.e. after a breakdown or accident when the battery is gradually running down, whereas the indicator flasher only ever has to flash two bulbs when the engine is running and the battery is fully charged. The indicator flasher also has a feature built-in that if one of the bulbs should fail it gives the driver due warning by the tell-tale and remaining bulb that side only glowing and not flashing. This is a safety feature so you know to replace the failed bulb as soon as possible, but more importantly be aware that other drivers around you may not know you are intending to turn and so take appropriate precautions. Unfortunately this feature renders the flasher sensitive to bad connections, and it doesn't take much to slow them down or even stop them.

The bad connection could be anywhere from inside the switch, the connections between the switch tail and the main harness by the steering column, the conenctors by the fusebox where the main harness joins the rear harness, where the main and rear harnesses join the tails on the light units, the supply tail to the bulb contact, the bulb casing to th brass bulb holder, the bulb holder to the light unkt casting, and finally the connection between the light unit castings and the wings they are bolted to (in the case of chrome bumper cars). Could also be a tired bulb. There may even be more than one bad connection, a new one adding to an old one to finally stop them working.

The correct way to tackle this is to bypass the flasher unit so the flashers stay on all the time both sides, so you can take voltage measurements and compare one side with another. Work out from the switch first one side then the other writing down the voltages in a grid. If there is a sudden drop in voltage between two points, or comparing the good side with the bad at a given point, then that is a likely cause. But work all the way through the circuits as there may be more than one.
Paul Hunt

Well, I've got it working now.

When I had the front right hand light unit apart, the back plate was basically made from solid rust, perhaps not too surprising given the lack of protection from road spray etc. Anyhow, the earthing looked like it would be rough through all the rust, and a seperate earth wire straight from the bulb to the bodywork confirmed this.

To avoid future problems I replaced the whole light unit (£12 / about $20US) and put the old bulbs in. Everything works fine, same flash rate on both sides - 17 flashes in 15 seconds, if anyone's interested.

So, thanks for the advice, and hope it stays working for another few years.

Andy
Andy Smith

This thread was discussed between 19/06/2008 and 25/06/2008

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