QuestionI have just put a '78 motor and overdrive transmission in my '72 Spitfire. This "new" engine has the Lumenition ignition system and in the "78 car it was connected to one of the large spade connectors on the alternator. Others have raised objections to this source to power the ignition system and I wondered where would be the correct point of connection.
Second question:
The old alternator had five connectors, the new has three. The old had one large spade connection (large gage Brown wire} another small spade connector (small brown wire 12v source) and two more small spade connectors that are linked (Brown/yellow stripe). Can you help me with what goes where and what is left out?
Third question:
Do all the wires on the positive side of the old coil transfer to the positive side of the '78 coil?
AnswerHi Pete,
The 78 had a Lucas / Opus ignition system which failed very often so may aftermarket companies started making their version of an electronic ignition system for the Spitfire. Each company designed their own wiring for their system. I don't know if they had designed it to take power from the large brown wire at the alternator or just the installer did that.
That was probably a easy place to pick up power. I can see why the others told you that was not a good idea. That post with the large brown wires on it is the charge wire for the battery and if there are more then one large brown wire the other is to power up accessories. The reason it is not a good idea is that if you get a poor connection anywhere on the large brown wire the charge rate (13.8v to 14.5v# will look for another route to get to the battery and then the ignition system will receive the added current and probably destroy the ignition system. It is amps not volts you have to be worried about.
The new 3 wire alternator uses one large brown wire #power to/from the battery# It also uses a small brown wire #also a power wire form the battery as a sensor for battery voltage)
On your wiring on the car you have a single small brown w/yellow tracer wire and a small double brown w/yellow tracer wire.
The small single brown w/yellow tracer wire is not needed so you can tape it up so it don't contact any power nor ground Or you can clip it off. Now take a 12v test light or a voltmeter and test the double brown w/yellow tracer wire for power. It should have none. Turn the key to the IGN position and it will show 12v on a voltmeter and if you use a test light it may light the test light dimly. If it does either of these while the key is on scratch the end of the brown w.yellow wire on a good ground and have someone watch the "IGN" light on the instrument panel and it should light up. This wire is the "Exciter" or "Trigger" wire that starts the alternator charging when the engine is running which then the terminal on the alternator becomes (+) and the light goes out. With the key on and the engine not running the terminal on the alternator is a ground which lights the "IGN" light. "IGN" name of the light is incorrect as it is not an ignition light, it is a "Charge" light.
There is a possible problem between the old and new coil. The Lucas/Opus used a 6v coil and a bypass system to power the coil from the starter solenoid to supply full 12v to the 6v coil only during starting and as soon as the key was released back to run the power to the coil on the Lucas/opus system then powered the 6v coil by a resistor wire thus dropping the voltage down to 6 v (under load) (disconnected from the coil it would test as 12v but under load it tests 6v.) Your 72 car had this system, however I have no idea what your aftermarket Lumenition system used, so you may have to search the Internet for the manufacture and request a wiring diagram of their system.
If the coil on the new engine is 6v then it used the same as your car. But if it is 12v you will need to alter the wiring of the ignition system of your car to use it.
If they tell you it is suppose to use a 12v coil and not use a by-pass resistor system let me know and I can tell you how to change your wiring of your car.
Howard
