QuestionI am working on a 1978 MGB. The ignition was changed to an Ignitor from the original. The wires to the coil appears to be the issue. When the starter engages, there is power to the coil, when it is in the run position, there isn't power to the coil. I have traced down the problem to the fuse block, it appears that #3 in the fuse block should have 3 wires coming out of it:
Brown to the ignition switch relay
Brown that turns to green to the radiator cooling fan thermostat
and the 3rd one should go to the resistor for the distributor.
I am missing the 3rd wire and the resistor. Is it possible to add the 3rd wire, put in a generic resistor and attach it to the positive side of the coil?
It appears that I have power to the #3 connection in the fuse block all the time. (2 green wires are hooked up to the the other side of the #3 fuse).
It also appears that the starter relay is working correctly. Power to 2 sides all the time and the white wire is active only when the key is in the on position.
AnswerHi Ben,
The original system used a low voltage coil (aprox 6v) The 12v system can not operate a 6v coil for very long so they designed in a system to only supply full voltage while in the "Start" position (White w/light green tracer wire) (which was then not full 12v anyway). As soon as the key was released back to the "Run" position the power to the coil was then run through a resistor wire (connected to the second White w/light green tracer wire on the coil)so as to supply a lower voltage to the low voltage coil.
The method was to run the power to the coil from a terminal on the starter solenoid that only was powered when the starter was operating. As soon as the starter was released the power to the coil came by a resister wire, thus dropping the voltage to the coil while running.
It sounds like while wiring in your new ignition system you have eliminated part of the original system. The original igniter used three wires, White, White w/black tracer and White w/blue tracer wire. The White wire was powered by #5 terminal on the fuse panel through a power resistor. This white wire also powered the power resistor and the resistor wire. The white w/blue tracer ran from the power resistor to the Ignitor in the distributor. The white w/black tracer wire went from the Ignitor to the negative side of the coil.
You need to look at the diagram that came with your new ignitor and look at the diagram of the car to see how to wire it up correctly. If you don't have a diagram of your car, go to my web site where I have posted one and copy it.
http://mg-tri-jag.net/78-80MGB1x1.jpg for the diagram
http://mg-tri-jag.net/78-80MGB21x1.jpg for the index
Howard
