Pre-electronic ignition polo's have a Ballast Resisted System feeding the ignition coil, meaning that when the car is running the coil is only getting 9volts instead of the typical 12volt replacement coils usually need.

(Heres a good explanation of why our old polos need a Ballast Resisted System:

http://www.minispares.com/Article.aspx?aid=154 )

I only found out recently after 2 years of running with unusual ignition issues. I didn’t think in a million years that my 12volt coil would only be getting 9volts.

But when my coil recently decided to stop working properly and i was getting misfire’s and a unwillingness to rev, i started to do alot of testing with the trusted multi meter.
It was soon apparent that my knackered 12volt coil had always been under fed causing a weak spark. After looking at the wiring diagram in the Haynes manual it clearly labels the coil being fed from a resisted wire.
(I have no idea why my coil started playing up, i think the problems are un-related)

Now for people still running the standard good old fashioned contact points and condenser system they should leave the ballast resistor system in place but they have to run a 9volt coil with it instead of the typical 12volts coil

On my polo I've now bypassed the resistance wire which downs the coil voltage down from 12 to 9 and now have a steady 12volts running to my coil.
(I'm running a transistorized setup with a TCI bosch coil which demands 12v)

My car has never worked better and the standard ignition timing setup now works properly where as before i had to run huge amounts of advance to make it run right(ish) due to the spark always being very weak.



Heres a simple 'How-To' to Replace the resisted 9volt cable so you can run a solid 12volts to your coil:

On the positive side of the of the coil theres two wires powering it, 1 black which supplys 12v only when the starter motor is cranking, and a purple and white wire which is a resistance wire that drops the voltage down to around 9volts when the car is running

The 9volt purple/white wire goes up to to the ,closest to the arch, connector block next to the fuse box (from memory 2nd from bottom right bullet connector)
This connects to a thickish solid black wire on the other side of the connector block behind the glove box which supplies the purple/white resistance wire with 12volts.

So this is where you connect up a wire to that black one behind the glove box and run the new wire through the bulkhead and connect it to the positive side of the coil, Then un-plug the existing 12/9volt supply

And that’s about it, wonderful 12volts going to your coil which will now be working at its full intended capacity

I will try and get a few pics up to help better explain things

This is really useful info for people with mk2s, I just checked the voltage to my coil, and it is 10.3volts and not 12. I've found the purple/white wire, and I am going to unplug the bastard and run a new ignition switched wire in as hypojam has said. I will take a few photos hopefully.

Be wary that your coil is probably designed for that voltage, the whole idea behind resistorised coils is to make for easier startring, when cranking the sterter motor sucks a lot of current meaning there is less for the coil, resulting in a weak spark (until the engine is running) The ballast resistor sytem uses a lower voltage coil and bypasses the resistor during cranking, meaning that the coil has the potential to see the full system voltage (but in reality sees more like the voltage it is desinged for) then when the car is running the resistor is switched back in and the coil gets full system voltage less that expended by the resistor. If you go to a non ballast coil then you will not have the advantage of higher coil voltage on startup, if you keep the stock coil and give it full system voltage then it will give a very strong spark, but not for very long, as the thermal load caused by the higher voltage will eventually destroy the internals.

Cheers, Dan

Hes converted over to a mk2 electronic ignition setup that uses a 12v coil

Yea the coil came from a late-spec ranger along with the ignition wiring harness and dizzy came from MH cars also. So I need the later 12v ignition switched wire.