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MG MGB Technical - Coil part no. for 77BGT

I have had a problem with the G cutting out after about 30 mins. The tacho drops to 0 and the the engine dies. I am running a pertronix electronic system. I thought it was the fuse box cutting power to the pertronix so I rigged a replacement fuse holder till a new fuse block arrives from the UK.

This hasn't fixed the problem. Today is started cutting out everytime I backed off the throttle after a 5Km freeway run. It would then fire up again as I tried to accelerate. I checked under the bonnet when I got home and found that the coil seems quite hot. It is a Lucas 15C6. My manuals all say a HA12 should be fitted. I looked in the archives and a thread called '2coils?' had quite a discussion going. This thread said that the 15C6 is in fact a 6 volt coil.
The car is a genuine English build. Does anyone know for certain what coil should have been fitted and how hot a coil should get after 30 minutes travel?

Ray BGT77

A bit more info. The Pertronix documentation says the coil should be 3.1 to 3.5 ohms for a 4 cylinder. The 15C6 currently fitted is 1.8 ohms.
Ray BGT77

Hi Ray.

If your Pertronix documentation states that it should be operated with a 3.1 to 3.5 ohms then you need a 12v coil which should be connected directly to a 12V ignition switched feed, not via a ballast resistor (which may be invisibly hidden in the loom in the form of resistance wire).

I believe that the coil numbers are (amazingly) actually helpful, in that the last part of the number indicates the intended voltage, with 6V coils being intended for use with a ballast resistor in 12V cars.

Having said that, I suspect that your problem may be elsewhere, coils do run quite warm.

HTH.. Don

I suspect you may be right. I put a new coil in and went for a drive up the local hill. Whenever I backed off the engine would die. When I applied throttle it would take off. I thought it might somehow be related to engine/gearbox movement and the angle of the hill.

I checked under the car and the bolt securing the earth strap to the gearbox cross member was loose. It was actually stripped so I replaced it and went for a drive back up the hill. No problems evident so I am hoping it was the bad earth.

Ray BGT77

This thread was discussed between 26/07/2005 and 27/07/2005

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