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MG MGA - Intermittent electrical fault

Of course it's always difficult to find an intermittent fault, but was just wondering if maybe someone has had something similar or can give me some ideas to try.
Moving home has meant I have hardly used the car this year but today I needed to take it out to make room in the garage. It happily started first time and I just drove out on to the drive. An hour later I tried to reverse it back in, but it wouldn't start.
I noticed the red ignition light didnt come on, but the horn and lights worked.
I had a look under the dash, didnt notice anything strange, and then found the red ignition light came on and the car worked absolutely fine.
I'm happy its working but nervous I may get caught out somewhere with no electrics.

Is the ignition key switch known for being temperamental? Or any other ideas? Thanks
Graham V

Graham,
general comments.

The lights and horn will be separate to starting.

Could be a loose wire or connection - have a look at where the wire comes and goes form red warning light and it's ignition path in the Driver's Handbook.

Switches can be kept 'clean' with use so if there's lack of use a rapid series of off/on switching (perhaps with the battery disconnected where required) may help to get them brushed up and going again.

All connections, wires and earths need to be clean, secure and protected.

Just disconnecting and reconnecting connections repeatedly can clean them up in the same way as the switches to get them going.

Its best to have all connections from the battery posts onward fully clean, secure and protected which could mean a little more effort to clean and protect with suitable materials.

After this you may need to track down the culprit or as you systematically go through checking, cleaning and rectifying you may come across the culprit.

Or if you really know how to use and interpret a (reliable) mulitmeter (I and many others don't) you could track down the issue(s) with that.
Nigel Atkins

Had this exact thing happen one month ago....In my case it was the connector that comes from the ignition switch to the main harness. Located under the drivers side dashboard. The pin for the power feed to the coil had a bad solder joint.. had to take it apart and re-solder.

problem solved.

the car was is a 1974 MGB GT.

Check the power to your coil and follow that wire back to the ignition...key switch.

Happy hunting and please post your results! :-)

S

Thinking about this--
It can't be anything to do with the coil wiring as that won't cause the ign light to malfunction -it has to be power to the switch, the switch itself or power out
If it's fixed itself as it has it is most likely the contacts in the ign. switch
--I was thinking contacts in the voltage regulator but that won't stop the engine from starting-just stop the light coming on
As Nigel suggested switch contacts are kept clean by use, there was probably a little corrosion or dry grease on the contact in side the ign switch and reusing it has wiped it clean
I'd be doing the 10-20 rapid on-off thing to make it all happy again and forget about it

I have the same issue with my elan, I get in and something won't work, last time it was the radiator cooling fan not working, gave the blade a spin and it hasn't stopped since
The heater fan motor was the one before that but I cheated and gave the heater box a hit with the air hose rather than pulling the heater out

Moral of the story --use it or loose it

willy
William Revit

Graham

I have had exactly the same in the recent past and have convinced myself it's something to do with the ignition switch internals. I find a couple of wiggles of the key always sorts it. Not yet got round to answering the question why, other than confirming all the terminal posts are tight so will be following this post with interest.

Steve
Steve Gyles

If you question the ignition switch during a failure, try this - put a jumper between the two fuses on the firewall. One is "power all the time" and the other is "power from the ignition switch". if the car the starts, its the switch or wiring to-from the switch.

This works when you misplace your key, as well.
Bruns

Where I put could be a loose wire or connection and have a look at where the wire comes and goes form red warning light in the Driver's Handbook I shouldn't really have put or meant ignition path as such. I was thinking of ignition switch and possibly the control box and dynamo for red light I'd also check and clean connections there, but I'd also look at the fuse box underneath and inside connections as well as the fuses as these car get furred up with time/storage and restrict how much electricery get passed them which might be the final straw for switches and connections further along.

I think if you start at the battery posts (with a battery fully charged and in good running condition) and then work along a circuit or wire at a time, perhaps staged over a series of work sessions, checking and cleaning/replacing as required you'll find and prevent problems before they get too bad.
Nigel Atkins

Thanks for your thoughts. It has really helped me think things through logically. And I do like Bruns suggestion about bridging the fuses.
Looking at the wiring diagram, it seems to me that as the lights worked, the power was reaching the "input side" of the ignition (key) switch without a problem. As power branches from there off to the lights.
So power must have been reaching that side of the switch.

Similarly there are two wires at the "output side" of the ignition switch. And I am pretty sure I didn't hear the fuel pump ticking over (as well as no red ignition light).
So it seems the diagnosis is quite simple - that power is successfully reaching the input pole of that switch, but not exiting from the output pole.

So that surely eliminates it right down to a bad contact on the ignition switch, either internally or externally?

One more complication in my case. I have adopted the clever design by Lindsay Sampford (thanks Lindsay) for an extra fuse box. Which will add the possibility of a faulty connection either side of the appropriate fuse.

Does anyone know if the ignition switch has a history of failing? I can check the other few contacts easily enough.

Thanks

Graham V

Yes ignition switches do fail. Sometimes if you can get to the innards you can clean and repair them.

If you're just looking to solve this problem for now, which is fair enough in the short term, then the problem is that it's intermittent. Go with trying the external connection and wire as that's the easiest to start with, try the wiggle test on both external wire and on connector.

If the red light flickers or goes out then you can thoroughly inspect this wire and external connections (on wire and switch).

If the problem is on the switch connector then the switch is coming out for closer inspection and testing - do very carefully note on paper or take photographs of which wires go to which connections and the orientation of the switch in relation to its fixed position and the wires on the switch. (I didn't do this thinking I'd remember the connections and then got mixed up and had to ask for help).

Obviously any work done on wiring is best done with the battery fully disconnected.

Nigel Atkins

Don’t be scared of a meter. This is all so much easier with a basic meter. I just set it on DC 20volts range and then check where I have live, I.e. approx 12 volts. Of course alternatively you can just use a bulb and wire for the test. Meter is also useful for checking battery voltage to indicate condition.

By the way there is short cut to ’jump’ the fuses by just putting one fuse between both sets of contacts so the one fuse does the job for both circuits. It is also useful if you loose your key. Unfortunately it is perfect for anyone wanting to steal you car.

Paul
Paul Dean

Problem is modern low priced multimters tend to be unreliable very quickly, usually one day after the guarantee runs out.

After the second one I got fed up, doing pre-testing check on the battery posts (always test the testing equipment before testing) the meter would take about 30 seconds to go from a reading of about 11.6v to 12.6v on a fully charged battery so I use it or nothing more than a continuity tester and it's not even great for that.
Nigel Atkins

Nigel
Must disagree with you on multi-meters. You must have been unlucky. I use mine all the time, not just on the car of course. By coincidence, only today I had to drill into a wall which I first checked out with my multimeter (it has a "no contact detector").
It told me that there was an electrical cable running up the wall from the power socket below (rather than down from it as I had expected). Worth its weight in gold just for that!
Graham V

Couple of other points.
I also carry a pair of lightweight leads with clamps on ends. Effectively jump leads for everything except starting which can be very useful in identifying faults And providing get you home fixes.

have copy of wiring diagram and codes in my tool box.

Nigel, you do seem to have been unlucky with meters. My experience has been as Graham’s. In addition to his household uses I also you it to check domestic batteries as quite often new ones can be down on voltage hence can save a lot of wasted time.

Paul
Paul Dean

"I also you it to check domestic batteries as quite often new ones can be down on voltage hence can save a lot of wasted time. "

A couple of years ago, I bought a PP3 (9v) battery for my expensive (employer supplied) multimeter and found it wouldn't work. When refitting the old battery, I measured only 6v on the new one!
Dave O'Neill 2

I find a test light quite good for this sort of problem --easy to poke in at places to see if power is there or not
William Revit

This thread was discussed between 04/05/2019 and 11/05/2019

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