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MG MGB Technical - Ignition woe- a different iteration

Hi all,

A few months ago I had a problem where my car died mid-journey- loss of power etc with no ignition light on to start. Cleaned up contacts on LT ignition side of things, and no issues since until yesterday.

Drove to work, no issues. At the end of the day, go to start the car up - turn the key and nothing - no ignition light etc. Interior lights work, and batteries are relatively new (a year or so old). Checked the spade connections immediately behind the ignition switch, repushed them in to check they were fully in - they all seemed solid.

Wiggled the whole harness, no success. After about 15mins turned key, got the ignition light on, but it didn't fire up when I turned the key to the last position. Turned key again but no ignition light. Tried pushing all the spade connectors more firmly into the ignition switch and then got the car started.

i haven't managed to replicate the fault since - so not exactly sure where the dodgy connection is. Is it likely to be at the ignition switch end?

Thanks

Nat

MGB 1973
Nat

Been there done that. Yes I would suspect the ignition switch. As I do not know how old your car's switch is, I would still get a replacement. I've done mine twice.

Cheers

Gary
79 MGB
gary hansen

Have you checked the earth strap from the engine block to the chassis?
Cheers, Charles
Charles9

If the ignition warning light isn't coming on then it won't be the ignition LT connections or the engine earth strap.

If the headlights come on, and stay on when you turn the key but still no ignition warning light or crank, then as you suspect, and Gary indicates, it is going to be the ignition switch or its connections. Because you sometimes get no warning light, and sometimes you get that but no crank (or clicking from the starter relay?) then it almost certainly is the ignition switch itself.

The switch is held in the lock with a very small grub-screw, as shown being unscrewed in the attached (UK 73). Check that is present and tight, and you can remove the switch to try turning it with a screwdriver to check if it or possibly the actuator in the lock is the cause.

More info here on working on the lock and switch http://www.mgb-stuff.org.uk/suspensiontext.htm#slock



paulh4

Thanks. I'm not sure how old the switch is, but I think it might be original, so circa 1973.

Would a dodgy ignition switch cause the car to have a sudden power loss (without jerkiness or any other sort of warning)- through breaking the circuit to the fuel pump, but still have the ignition light come on?

I'll have a look for the grub screw- is it possible to remove the switch in situ without taking off the steering lock?
Nat

Yes, but it will be the loss of power to the coil that causes the engine to die, not the fuel pump. The carbs being full of fuel will keep the engine running for some time after the pump has stopped operating.

The fact the ignition warning light comes on when the engine cuts out shows that the problem is loss of voltage from the ignition switch, and not something associated with the coil or distributor. If the warning light DIDN'T come on when the engine cut out, but works as it should otherwise, then it shows there is still voltage coming from the ignition switch, but it isn't reaching the coil and distributor.

Yes, you can remove the switch with the lock in-situ.

paulh4

This thread was discussed between 27/10/2017 and 30/10/2017

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