My MG starts up good it runs for about 20.

WITHOUT DOING SOME TESTING

(IF YOU HAVE A MANUAL, IT'LL PROBABLY SHOW YOU HOW----AT MINIMUM, YOU CAN FIND THE "VALUES" YOURS SHOULD HAVE)

YOU TUBE IS A GOOD PLACE TO GET IN A LITTLE "MONKEY SEE---MONKEY DO"......YOU WILL NEED THE VALUES YOURS SHOULD READ

IT REALLY SOUNDS LIKE AN IGNITION RELATED COMPONENT.............MY BEST GUESS IS THE IGNITION COIL ! ! !

IF YOU HAVE BYPASSED...OR SOMEONE ELSE BYPASSED........OR JUST PLAIN OLE ELIMINATED THE "BALLAST RESISTOR" (ALSO FOUND IN THE LINK BELOW)............

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/PartSearchCmd?storeId=10151&catalogId=10051&pageId=partTypeList&suggestion=&actionSrc=Suggest&langId=-1&searchTerm=ignition+coil+components&vehicleIdSearch=19953&searchedFrom=header

............THE COIL MAY BE GETTING TOO MUCH JUICE (FULL ALTERNATOR/ BATTERY VOLTAGE)

......IT OVERHEATS

........AND PRESTO !!!

......YOU ARE "AFOOT" !!!

THE BALLAST RESISTOR (REPLACEABLE PART) OR A "RESISTANCE WIRE" (ON SOME VEHICLES, PART OF THE WIRING, TAKING THE PLACE OF A "B.R.") LOWERS THE VOLTAGE TO THE COIL.....AS TOO MUCH, WILL DAMAGE THE COIL

I HAVE BYPASSED SEVERAL BALLAST RESISTORS----WHEN THEY HAVE BURNED OUT----AND THE "AVERAGE BEAR" WOULD BE AFOOT, AS NO POWER COULD REACH THE COIL.

A "BYPASS" COULD BE JUST CONNECTING THE WIRES ON EITHER SIDE OF THE "B.R."JUST TO BE ABLE TO "LIMP" HIM HOME! (A TEMPORARY "GO")

ANOTHER POSSIBILITY IS YOU HAVE THE WRONG COIL

SOME HAVE INTERNAL RESISTORSSOME DO NOT........IF YOU JUST REPLACED IT........MAKE SURE IT IS THE CORRECT ONE!

I'M SHOWING YOU SOME PICS FROM BOTH OF MY JEEPSBOTH OF MINE HAVE BALLAST RESISTORSI HAVE REBUILT AND UPGRADED THEM

PIC EXPLANATIONS BELOW

PIC 1) THE BALLAST RESISTOR IN MY 1946 WILLYS........DROPS MY VOLTAGE DOWN AROUND 7 VOLTS (SAME FOR MY 1977)

PIC 2) I RECENTLY UPGRADED MY 1946 WILLYS WITH A ELECTRONIC IGNITION MADE BY "PERTRONICS" THIS ONE IS SPECIFICALLY FOR MY DISTRIBUTOR........THE COOL THING IS, SHOULD IT GIVE TROUBLE, I CAN PUT MY POINTS SYSTEM BACK IN, IN UNDER 10 MINUTES!

PIC 3) YOU CAN "TWIST" THE WIRES TOGETHER/ USE ALLIGATOR JUMPER WIRES/ OR DO IT LIKE I DID, USING A PIGGY BACK CONNECTOR..............TO GET YOU BACK HOME, WHEN THE RESISTOR HAS BURNED OUT

PIC 4) THIS IS NOW "PIGGYBACKED" (MY BALLAST RESISTOR IS STILL GOOD)BECAUSE I DON'T NEED THE BALLAST RESISTOR W/ MY NEW IGNITION, I LEAVE IT PIGGYBACKEDSHOULD I HAVE TO REVERT BACK TO MY POINTS.....I WILL UN-PIGGYBACK IT.....AND USE THE "B.R." AS I HAVE IN THE PAST W/ THE POINTS (SO FAR, THE NEW IGNITION HAS BEEN A GIANT IMPROVEMENT OVER THE POINTS)

PIC 5) MY 1977 JEEP'S COIL AND DISTRIBUTORI UPGRADED IT UP FROM A "PRESTOLITE IGNITION" TO A "MOTORCRAFT" IGNITION SYSTEM (MOTORCRAFT WAS ADOPTED IN 1979 [2 YEARS LATER THAN MY MODEL] AND IS A MUCH MORE DURABLE SYSTEM) ..............SINCE THE '77 ORIGINALLY DID NOT HAVE/ OR NEED A RESISTANCE WIRE OR A BALLAST RESISTOR, WHEN I "UPGRADED", I HAD TO USE A DIFFERENT COIL AND DISTRIBUTOR.........THE "B.R." IS UNSEEN IN THE PIC, IT IS A FEW MORE INCHES TO THE LEFT, MOUNTED ON THE FIREWALL.......BOTH THE '77 ARE '79 IGNITION SYSTEMS WERE ELECTRONIC, MY '77 JEEP DID NOT HAVE POINTS AT ALL, AS WITH MY '46 WILLYS

PIC 6) 1977...."MR. JEEP"

PIC 7) 1946...."WILLY"

I HOPE THIS "SORTA EXPLAINS" STUFF TO YOUREMEMBER, MY JEEP AND YOUR CAR ARE NOT EXACTLY THE SAME UNDER THE HOOD

LET ME KNOW IF THIS DID SOMETHING FOR YOU!

THE MEDIC

WELL. PIC 1 DID NOT MAKE IT ON ABOVETHOSE ARE NOW 2 THRU 6

IT'S THE SAME AS PIC 2---'CEPT THE WIRES WERE HOOKED ON EITHER END OF THE BALLAST RESISTOR

THE MEDIC