Triumph Repair: Coil, ballast resistor, roadster factory

Question
QUESTION: I own a 1974 Spitfire. I decided to replace the coil since the one one the car looked original. As I was taking off old coil I noticed a small condeser next to the coil connecting to the coil. Well, there is a condensor already in the distributor. Guy at auto parts place told me it's just a noise supressor for the radio. Since I don't have a radio(and his idea was right) I don't need to put the little condesnor back on. Do I ??.I should just need the two connections negative to distributor and positive toward ignition. Why are there more possible connections(clips) on coil? To make me nerotic??Did that make sense? Thanks Jim

ANSWER: Hi Jim,
If it had a condenser on the coil it was most likely a radio noise suppressor and you don't need it if you don't have a radio. The extra clips (spade connectors) were not put on there to make you neurotic, They were put there to make you think you might be neurotic. If you replace the coil make sure it is the same ohms on the primary side of the coil. If it is not written on the coils check both with an ohm meter before you use it.
Howard

---------- FOLLOW-UP ----------

QUESTION: Howard. First-Sorry for this long winded question. I bought the coil from Roadster Factory and it said it was for a Spitfire.You said make sure it is the same ohms on the primary side of coil.Which is primary side of coil ?? You lost me there. Shouldn't this coil be "ready to go" I don't own an ohms meter. And to become more neurotic one British parts supplier(Victoria British) shows a ballast resistor next to coil--other parts catalog(Moss Motors) doesn't even show it or mention it --who's right??? Someone told me I could cook my electrical system without balllast resistor. See how easy it is to be neurotic about this  Can't they just say you definetly need this part or you don't. Seriously though what's with the ballast resistor? Should I have one. The little condessor I first mentioned in first question to you is small barrell shaped looking thing with 150V stamped on it. Could that be the ballasst resistor or just the radio noise suppressor. How's that for a question? I'll also check my shop manual for wherabouts of the ellusive ballast resistor Thanks again. Jim

Answer
Hi Jim,
I know all that can be confusing partly because the original system used a ballast resistor wire instead of a normal ballast resistor mounted on the coil. A small can shaped single wire unit like you described is a condenser, most likely put there as a radio suppressor and that can be discarded. Any number of ignition systems could have been installed on that car since it was new. Here is what to do to be sure,
Volt/Ohm meters are not expensive and a tool you will get to use many times if you are going to work on your own car. Look at the available volt/ohm meters VOM)at Radio shack or such a place and get one.
Measure across the two small wire connections on the coil with the wires disconnected from it and the VOM set to a "Low Ohm" scale. Write down the readings and check the new coil the same way. If they are close, install the coil and have some one try to start the car while you take the VOM (set to 0 to 30 or what ever the scale in "DC Volts" that will allow you to read from 6v to 12v) connect the positive lead (red) to the (+) connection on the coil and connect the negative lead (black) to the case of the coil or to the engine. (ground). With the engine spinning, it should read from 9v to maybe 11v on the meter. Have the person release the key from start back to Ign. and read the VOM. Now it should read less, maybe 6v to 7v.

Resistors are used to drop voltage. The way this system works is, A battery normally has 12v available but when a starter is engaged the starter uses a lot of current which drops the voltage available to the coil. If you use a 12v coil it would not fire when you only have 9v left over while the starter is used. A 6v coil would fire just great with only 9v, but when the engine started and the starter was no longer in use you would have 14v (alternator charging now) and that would over heat the 6v coil very quickly. So they add a resister in the line that powers the coil when running and bypass that resistor when the starter is working. Some cars use a large resistor mounted on their coil but this Spitfire used a resistor wire.
This is all the tests I outlined above because your system could have been changed many times since new.
If you know how a system works, it does not matter how many times it was changed, you will be able to fix it.
I hope this helps, Print it and follow it exactly and let me know.
Howard