MGB 1977 GT ignition problem

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woodman
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Joined: Sat Jun 01, 2019 4:02 pm
Forename: Mick
Surname: Smith

MGB 1977 GT ignition problem

Post by woodman » Mon Jun 03, 2019 8:57 pm

Left ignition on overnight ....flat battery....Charged battery...car started ran for 20 seconds STOPPED....then found fuel guage, fuel pump ,ignition light NOT working.....put petrol into carbs engine started ran for 20 seconds STOPPED....checked fuses ...earth straps...fitted new ignition switch...STILL Same .....everything works except fuel guage ,petrol pump, ingnition light .....any ideas.....please.....Mick
Vic Butler
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Re: MGB 1977 GT ignition problem

Post by Vic Butler » Mon Jun 03, 2019 9:29 pm

Does the engine cut out abruptly or splutter to a stop? What does the rev counter do and have you checked for a spark at the plugs after the engine has cut out and does the fuel pump tick then stop with the ignition on?
I'll have a look at the wiring diagram to see if I can find an electrical link between the fuel gauge and fuel pump. The ignition light should remain on until the voltage across its terminals from the alternator equals battery voltage. It's possible the bulb may have blown so that's worth checking because the alternator won't charge if the bulb is blown.
I'll report back later re the pump and gauge.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
Vic Butler
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Re: MGB 1977 GT ignition problem

Post by Vic Butler » Mon Jun 03, 2019 11:09 pm

I've had a look at the wiring diagram. It appears that the feed to the fuel pump goes via the white/brown wire to the ignition light bulb and the brown/yellow wire from the bulb goes to the alternator. The fuel gauge light green/green wire goes to the voltage stabilizer and the green wire from there goes to the wiper/washer switch. There is a wire from the wiper/washer switch to the washer pump and a green wire goes to the fuse box. Check the fuse that has 2 green wires on one of its sides. Does the windscreen washer pump work?
It's odd but it would seem that if the ignition light bulb fails the fuel pump won't work. The pump isn't fused.
I hope this helps.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
Vic Butler
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Forename: Vic
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Re: MGB 1977 GT ignition problem

Post by Vic Butler » Tue Jun 04, 2019 7:53 am

I omitted to say how to test the fuel gauge. Disconnect the wire from the tank sender behind the offside rear wheel and with the ignition on check with a meter there is 12 volts. If there is then short the connector to earth. The gauge should rise to full. If it doesn't the fault is with the gauge or the voltage stabilizer.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Charles Farran
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Re: MGB 1977 GT ignition problem

Post by Charles Farran » Tue Jun 04, 2019 8:56 am

On your first post you said you had left the ignition on all night.If the L.T. leads to the coil were left attached, then you may have burnt out the coil which may be adding to your problems.
Cheers, Charles
1980 Roadster
Vic Butler
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Re: MGB 1977 GT ignition problem

Post by Vic Butler » Tue Jun 04, 2019 11:06 am

As Charles says it's likely the coil could cause problems as it's overheated. Best replace it but make sure you get the correct one for the ballast resistor ignition system.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
woodman
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Forename: Mick
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Re: MGB 1977 GT ignition problem

Post by woodman » Wed Jun 05, 2019 5:33 pm

thanks to all for replys will check them out at week end ....thanks mick
Vic Butler
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Re: MGB 1977 GT ignition problem

Post by Vic Butler » Wed Jun 05, 2019 9:50 pm

Mick, please let us know any results.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
woodman
Posts: 3
Joined: Sat Jun 01, 2019 4:02 pm
Forename: Mick
Surname: Smith

Re: MGB 1977 GT ignition problem

Post by woodman » Wed Jun 12, 2019 12:18 pm

Hi...problem sorted ....a previous owner had some fancy sound system fitted ,when it was removed he left the dodgy wiring in causing a short so after removing it its now ok....thanks for all replys mick
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