MGB & GT Forum

I've been having some trouble with my MG's ignition system. Usually the car will start right up and I will be able to drive it for a short time and then she will start running rough and die unless I keep reving her. Once she dies she can be incredibly difficult to start again. Sometimes I have to let her sit for hours before she'll fire back up. I've been monitoring the voltage on the battery and she has plenty of voltage. She'll act like the battery is dead but the battery is fully charged. I replaced my ignition switch within the last year and a half or so and it's acting up. The car will even sometimes fire up when I turn it all the way to the off position. The other day I bumped the ignition switch with my knee while getting in the drivers seat and the car started to fire up and the key wasn't even in the car. I'm very confused, maybe I just got a bad new ignition switch and should start by replacing that again. I have included a video to better demonstrate what is happening



The ignition light on the dash also stays on while the car is running. I've never thought much about this because its been like that for years but could this be an issue?



Any help would be greatly appreciated!

Thanks,
Austin

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1978 MGB
Weber Carb
Moss Motors TT Full Exhaust
Custom Lowering Kit
26k original miles

Check to make sure you have a vented gas tank cap.
When it will not start take the cap off and see what happens then.

Mike



Edited 1 time(s). Last edit at 2015-03-31 11:42 AM by MallardMike72.

thanks Mike, I'll give that a try



Edited 1 time(s). Last edit at 2015-03-31 04:35 PM by Atill93.

You probably have a bad ig switch. Otherwise, you have wires hooked up wrong (not even sure that would create your issues). Yes, you should fix the ig lamp.
Make sure the wiring at the starter is clean and snug.
Heat increases resistance. Loose connections become non functioning junctions.

Check your coil. Is it "hot" after running? Check the primary and secondary resistance values. Primary between +/- poles should read .5 - 3 Ohms. Secondary between coil tower and + should read between 6K - 15K ohms. If it's too far out from those numbers it's probably bad. Measure it "cold" before you drive and "hot" after. If the coil is actually too hot to touch...again...probably the coil.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

So i've replaced the ignition switch and now the car won't turn over at all
now i've got to figure out if it's something electrical or if I need a new starter...

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1978 MGB
Weber Carb
Moss Motors TT Full Exhaust
Custom Lowering Kit
26k original miles

There are so many possible problems that a single solution is difficult to make remotely. I will throw out one and frankly likely NOT it. When you removed and replaced the ignition switch what condition was the plastic paddle between the key and the switch. I have seen them with edges so worn that it will hang up inside the new switch. Your starter is likely fine. A good start for beginners is investing in the book MGB Electrical System by Rick Astley. Its well written with a guide to solving common MGB electrical problems. Its not a generic car electrical system book it all about specific MGB electrics US and UK. It is a real life saver for people who are beginners. It will show you how to check for starter problems, switch problems best of all it is comprehensive for all the MGB year changes. Moss has it.

thanks for the recommendation John, I think I'll order that book today

You can easily bypass the ignition and test the starter and solenoid with a jumper wire. once you know the starter works you can then check the switch.Are you sure you got the correct replacement?

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ended up starting the car by running a hot wire straight to the starter
weird thing was I couldn't get the car to start when I ran power to the brown and white wire that hooks up to the starter

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1978 MGB
Weber Carb
Moss Motors TT Full Exhaust
Custom Lowering Kit
26k original miles