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MG Car Repair/no power to the electonic ignition distrubtor


QUESTION: i have power to the coil and to the amplifier both are new. i did just use a 12 volt coil.could the pickup coil in the distrubtor be bad? and how would i ck. to see if it is good. it is a 1977 mg midgit.

ANSWER: Hi John,

If you still have the original ignition system, you have the Opus / Lucas ignition. This is a box mounted on the side of the distributor and the vacuum unit is mounted on it. The pick-up inside is wired directly to the box and the box has three wires to the harness.

The coil should be a 6v coil not a 12v coil. The 6v coil is powered directly by 12v form the starter solenoid and as soon as the engine starts and the key is released back to the run position the 12v from the solenoid is cut off and the ignition switch then powers up the coil by way of a resistor wire which drops the available voltage down to a voltage that can operate the 6v coil without over heating it. The box (control unit) receives it's power from a small ballast resistor called a "Drive Resistor" (checked with an ohmmeter at about 9.5 ohms)

I found very few bad pick-ups and I could not find a quote on the resistance as it is nothing but a small coil. However on every bad one I found they were open circuit and all the good ones had some resistance.

While working in the MG dealerships I found that most of the Opus / Lucas systems failed more then once in the 12 month warranty period. So it is rare to find one working on an MG now 37 years later. This prompted many aftermarket companies to produce a replacement ignition system so you first need to ID what you have. The easiest way is to look at the pick-up wires to see if they go directly into the box mounted on the distributor. If they do, you have an Opus / Lucas system and the above is what to do to test the system.

However if the wires from the Pick-up leave the distributor, it is an aftermarket system and you need to ID it first and contact the dealer of that system for a diagram of how it is wired. (Most that I looked at still used a 6v coil) only a few used a 12v coil but they had to change the wiring of the car to match it.


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QUESTION: this one must have been changed out. it has a ingnition amplyfier box that has agreen wire and a red wire going to the distrubtor. also wires that go to the coil, they are white with a green stripe going to the hot side of the coil. and white with black stripe going to the neg. side of the coil.we put a new wiring harness on ,every wire swoped out with each other. i made sure they were connected all the way.after reading your mess. i remember that there was 3 wires that didnt go to any thing.2 of them are coming out of the firewall with the fuse wires but they were about 18 in. longer.with the key off one of them is hot but when you turn the key on power goes off, the other wire isnt far from the dist. i put a inline fuse between the other 2 and it powered up the 3rd. so i beleive this harness was to a resister and the other must have gone to the clynoid. but since its been changed do we need these? i put the coil back on . we just tried a new amplyfier box, no differnt. that was 300.00! about to give up! please help!

Hi john, The trouble is that there were half a dozen different companies making electronic ignition systems to replace the Opus / Lucas that came on the car and each had a different wiring for each. I worked for the MG dealerships and we could only use the OEM equipment (Opus /Lucas) which failed too often. I only know the MG system and the car.

If you bought a new amp you should have received a diagram of how it is suppose to be wired. Plus you should now know what brand it is. Take a photo of the diagram that came with the amp and I can tell you how to wire it to the car. If you didn't get one you need to contact who ever you bought it from and tell them you need to get a diagram of how to wire it up. Your red and green wires are not MG. MG never used green nor red wires anywhere on their ignition systems. All British cars used Lucas and they were consistent on color codes. For example all red wires on every brand of British car were only used on small light bulbs like instrument bulbs and some side marker bulbs. All green wires on all brands of British cars were used on accessories only.

We have to know what each wire does so we can connect it to the correct wire of the car. You have to know what wire does what so as not to connect a wire to 12v that is not suppose to got to 12v and the same is true for grounds. Some aftermarket units had the amp as the pick-up and others had a pick-up and an outside amp. Some had a pick-up that was an LED and had a disk that mounted on the distributor shaft with fine slits in it. Connecting any of these up wrong can destroy them and almost all auto parts stores will not take any electrical part back once it has been installed on a car.

Get the diagram to me and the brand of system it is and I can tell you how to connect it to the car. This is not something you can guess at.


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Howard M. Fitzcharles III


MG from 1956 (USA versions only) up and Engine theory.


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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