Coil confusion

[Forkie]

So today i decided to boot everything else into touch and have a day on the car. Waterpump and another set of new hoses fitted. Rocker cover off as i wanted to have a general look under there, and to check valve clearances. Could not believe how clean the under side of the cover was, not even any staining. Cannot remember now if i had done the clearances before, but there were a few that seemed about right, a few more that i thought seemed a tad tight, so hopefully got them right across the set now ( got too late to fire it up this eve).
So to the above question - have been browsing back through some of our 'annuals' and regarding one of Mike 'quick tip'Allams tests on coils , April 2022 - another job i did today. So his first test was the positive in the king lead to a low tension - he states anything less than 5 - get shot. Mine reads 4.5.... the other test was the pair of LT - i got 0.0 !!!! I assume my meter is correct.... anyhow as i have never replaced the coil might as well do that as well. Quick look at C.W. site - he lists a 6V or a 12 V Sport with ballast resistor. Which should my '75 S have?? I am on the understanding i should have the 12V ballast type, but the pic on his site showing the old and new type, i dont recognise the old type resistor at all. What i have on my engine is , to the left of the coil, bolted to the block , a cylindrical ,almost condensor looking item, nothing like the old style ballast resistor Chris shows. Basically i am asking what do i need to buy - which coil, and b.r. or not.... standard factory set up / points etc.
Many thanks in advance.

[Alec]

Hello Forkie,

later cars had a resistance wire incorporated in the loom, (white pink possibly from memory) rather than the rectangular ceramic reistor .
There will also be a second small wire coming from the starter motoor if your car is a ballast ignition one?
I'm sure someone else will be along with more specific knowledge of your model and year.

Alec

[Charles H]

Alec is correct. The little cylinder you describe is an 80's or 70's addition to suppress the radio interference. Just bin it. An S has the resistor wire built into the loom, and is as Alec states, white/pink. You need the 6v coil, the system runs on 6v when running hence the resistor wire. When starting the starter circuit puts 12v to the coil to help get a bigger spark. Continuous use of 12v across this coil will burn it out.

[Forkie]

Ah right , i did think this morning radio suppresor - long time since i had that in my mind!! Ok ideal, so its just the 6V coil required then. Thanks again chaps

[johnnydog]

If you source a replacement coil elsewhere, if it is a ballast 6v coil, it should have a sticker on the body of it stating (from memory) use with ballast of 1.3 - 1.5 ohm resistance, or similar. Used coils often loose part of this sticker after contact with the coil clamp, but you usually can make out the fact it is a ballast coil.

[Forkie]

My new coil from CW arrived on the morning that we were off on a long weekend break, so i just had chance to open up the box and check the reading of that to the one fitted on the car ( for some odd reason i can only perform one of the two tests which is the king lead / low tension test) - the one on the car reading 4.5 , the new one was over 8 - so that gives me a little justification that it was worth buying a new one, and im keen to fit and see if it makes it run any better. Incidently im sure on the new coil there is a sticker reading ' 9V ' which made me confused again !!!! But on the bill it states ' 6V for use with ballast resistor' so im sure i have ordered, and Chris has sent the correct one .

[Alec]

Hello Forkie,

the resistance measurement should be the primary winding i.e. between + and + .
I don't understand why you say that you can only do the primary to secondary?

Alec

[Forkie]

Hi Alec, i dont really know? !! Following Mikes 'tip' - on putting the positive connector into the King lead apperture, and the negative on to either secondary i got a reading of 4.5 - which according to Mike i should of thrown it away last week, hence the purchase of the new one, which reads over 8. Trying the secondary to secondary test, both coils i get no reading - as in 0.0 !!!! Cannot think what i am doing wrong, i even tried moving the switches about too !!! The single reading was enough however for me to replace. It probably is the original coil, again!! Not had chance to swap and try yet. Will let you know if it 'feels' any different.

[Alec]

Hello Forkie,

using a multimeter, I take it on the correct ohms scale (Not Kohm for instance) there should be a measurement between positive and negative terminals. That is the primary circuit (A tip, when doing resistance measurement short both leads together which should read zero, if not that has to be added to any device measurement. Older meters like AVOs had a knob to zero the resistance scale). Between the king lead to say positive should give a much higher reading and on the other negative to king lead should give a slightly very higher one. It may be the other way round depending on the internal connection. The HV side is the secondary and one end of the winding is connected to one of the primary terminals. So measuring king lead to one terminal will just read the secondary winding resistance, the king lead to the other will measure bot windings in series so be slighly greater in resistance.

I hope that hasn't made it more confusing?

Alec

[Forkie]

Alec - in short - yes it has Give me a Vauxhall 24 valve V6 engine to rebuild the metal work on and im your man - basic electrics though elude me
So just been under the knife at the dentist so looking for something ' easy ' to do. So read your post, dug out the relevant ' quick tip' mag ( issue 244) , new coil and multimeter, all laid out on the proverbial kitchen table ( good job the better half is still at work) just to go through it all again.
So the multimeter i am using is the Draper Digital type, # 50023. I have the top switch fully to the right. Lower switch up on notch 2 , for both tests. So it is a completely different type to what Mike is using - i have switches, he is using a dial type. As i read his tip, both tests are using the same settings - 200k. As the first test made sense, on both coils, as in the one on the car reads far lower than the new coil, i am thinking i have this in the bag. Until the second test....
So just redone it again - so test one, positive probe in kinglead, earth probe to l.t. - reading is 8.4. Keeping positive in kinglead, but swapping earth lead to the other l.t. - same , 8.4. Test two - using just l.t. connectors - either way round, same result - lots of quickly jumbled up numbers until it settles down - final reading - 00.0
I get the same reaction when i touch both multimeter connections together, ending up with the same 00.0. I would hazard a guess my multimeter is playing up, but test one seems to be ok, and makes sense.....