When I replaced the coil, I took the 2 black leads connected to the old coil -ve and connected those to the new coil-ve and took the 4 red leads connected to the old coil positive and connected those to the new coil positive. Is that wrong?
More than likely. There is no standard VW red wiring on the coil so what you describe could be anything.
As @zedders says, none of the wires on a stock coil is red. All of the black wires in a VW installation are ignition switched 12 volts - it is the VW convention, just like brown wires are chassis connections. The connection to the contact breaker and condenser is often green. So, while it might have been the coil failing when it broke down, it is almost 100% certain you blew the electronic module in the distributor if you put all the black wires together, and all the red wires together. Just feel a little sad not ashamed, I have done this too.
The only thing I guess I could have done is assume the 2 black leads from the old coil were -ve because they were black and not looked at the terminal label in the coil itself. This COULD have happened as I would have definitely assumed black was -ve and there were 4 red wires which I would have assumed were +ve. I presume with the ignition on I should be getting a reading from a multimeter at the -ve and +ve terminals of the coil? (I’m not)
The coil positive and negative connections are not particularly important with respect to polarity - the engine will run with the coil low voltage connections either way round. The electronic module on the other hand does not like driving into a short circuit, there is no protection in the design, and that is what happens when the black wire is connected to the ignition feed, its trying to ground 12 volts when it gets triggered, either as you first turn on the power, or if the engine is rotating. It is all a pity - a few years back there were ignition coil driver components sold by the likes of ST Microelectronics that detected short circuits and flagged a fault. But these kind of things go into the likes of black box electronic ignition circuits in the ECU of the car. The little modules we buy are compromises to fit in the space available - if you look at things like the MSD6AL CDI box, they are quite chunky units. And they break also. The 123 distributors also fix the problem by being better designed, better built and more expensive , and using more of the volume of the distributor for electronics. While Pertronix are over priced cheap stuff, and Accuspark are lower priced cheap stuff. With ignition on, one end of the coil (black wire) should be positive to chassis, if it is not then there is another wiring problem, as the power feed to the coil positive is an unfused 12 volt feed - loop from battery to the ignition switch and back to the engine bay. The other end of the coil should also be positive to chassis, but if you have blown the ignition module, you may have to disconnect the module from the coil before it stops shorting it permanently to ground. If there is no current flowing through the coil, there will be no voltage across it, so if the module went open circuit, the voltage will be 12 volts at both ends of the coil going to chassis.
OK so what you’re saying is I need a new distributor? Or at least the module inside the distributor which I probably wouldn’t have a clue how to replace without replacing the unit. This is really gutting as it took me ages to work out how to replace the distributor and tune the engine. I still don’t understand how I could have done this though as I grouped the coil wires together in exactly the same way for the new coil as they were in the old one. How could it have shorted it, as I had been driving round like that for the past couple of weeks with the old coil. I guess the only thing is, as I said if the black ones were going to the +ve coil terminal in the old coil and then I rewired them to the -ve terminal in the new coil. I really don’t understand electrics well. I can’t think how else it could have happened. I didn’t just decide to group the red ones and the black ones together for the new coil terminals, it was how they were fixed to the old terminals.
The only useful measurement you can make is getting 12V between the +/15 terminal of the coil and the crankcase with the ignition turned on.
We have all done it and thought 'how is it possible that I've done that '. I thought I'd been very careful but still got it wrong. I bought a new module, easy to fit, and trying to be extra careful in future.
To be fair nobody knows this HAS happened, we're guessing on the internet. Your 2 black wires could be rev counter and ignition module, your 12v feed to the coil could have been repaired with red wire after the PO decided that would stop HIM accidentally destroying another ig module. In that case we're missing real problem whick might even be your ignition switch is duff. Perhaps you can trace a few wires.
Looking at your oil coil picture your wiring is a mess. I think the +ve supply is the thicker red that's extending an orange wire - further along hopefully it morphs into thick black. The black with a pinkish connector cover is Pertronix The other black is actually black with red stripe and should be on your rear lights so who knows what's happened. I recommend someone who is very familiar have a look for you, you'll struggle with a diagram if someone has changed things like this.
Yeh it is a bit of a mess. I forgot I had taken that pic before but it confirmed that I had transferred over the 2 black wires from old coil-ve to new coil -ve and the 4 red wires from old coil +ve to new coil +ve correctly. The 2 blacks are Pertronix dizzy and the black and red one. You say this should go to the rear lights? It doesn’t seem to. What should it be? For the 4 red ones, there are 2 thicker ones - the one that extends an orange wire goes to a junction near the fan and comes out as a black and brown and then the one with the yellow sleeve which could also be the ignition +ve goes downwards and changes into a black one. The other 2 thinner red wires, one is the dizzy one but no idea what the other one is. Though after checking everything was connected OK I’d realised I’d left the wing connector on the +ve coil terminal which I didn’t need as the red wires all have loop connectors on. I took it off so I would get a better connection and tightened up the nut on the +ve coil terminal and the +ve terminal has now sheared off so I have to order a new coil anyway now.
While you’re waiting for your new coil, trace all of those wires back, one at a time, to see where they come from. That’s such a mess, it’s impossible to see what’s what.
Yes, will do. There are a couple of Accuspark coils on Amazon Prime. Does it matter if I get a 1.5 or 3 ohm one?
Otherwise it goes pop as the transistor inside it gets very hot with a low resistance coil, and then you head into the "hot Pertronix" twilight zone. If you still have your original distributor, (and the garage didnt nick it .. OK just re-read original posting) when the Pertronix was installed, now is the time to re-fit it and check the coil works with a basic points ignition. Apart from needing regular checking and adjustment, and providing new points and condensor from time to time, a points ignition works pretty well.
On the wiring diagrams, that colour coded wire is used for the rear lights and nowhere near the coil at any point. That's what I mean - your colours are all mixed up, maybe someone re-used that wire for something else. This is only going to confuse you and us unless as Snotty suggests you trace the wires and draw a diagram.
OK, so it’s possible the coil I had wasn’t compatible with the new SVDA distributor. I do still have the old distributor.
