7 replies to this topic

[robze]

well my mini city e auto 1991 has decided not to play. it has a ballast resistor wire going to the coil. now for some figures. there is 13.96v in the battery. 5.94 at the coil with ignition on but when cranking this drops to 3.12. what does this mean??? im all confused. i thaught it was meant to go up during cranking.
thanks
rob

[Cooperman]

Bset advice is probably to get a 12V coil for about £13 and replace the 'pink' resistor wire with a new standard wire from ignition switch to coil. That way you get a more reliable ignition and remove the risk of the 'pink' wire burning out and taking most of the engine bay loom with it (as has happened in the past).

[Ethel]

Check that there's also a (yellow/white) wire running from the starter solenoid to the coil and it's live when the engine is being cranked. If you have a multimeter you can check the resistance of the ballast wire by putting one probe on the coil end of the wire and the other probe on an ignition feed (white wire on fusebox) with the ignition turned off. You should see about 1.5ohms.

[robze]

i will check the wires tomorrow. can you tell me more about how to do this 12v coil conversion??? or atleast temporaryly till i can sort the problem.
thanks
rob

[Ethel]

The voltage doesn't sound bad. Ballasted ignition was introduced for reliability and what you've reported kind of illustrates how.

Because the starter is such a huge current drain the voltage drops when it spins. Ballasted ignition has the resister wire so it always runs at reduced voltage. The extra feed from the starter bypasses the ballast wire so the only reduction when the engine is cranking is due to the starter which roughly matches the ballast resistance and the coil gets the same volts. yours is probably showing a further voltage drop because the bypass feed isn't there.

It could also be a poor battery connection or earth adding resistance.

[lrostoke]

i will check the wires tomorrow. can you tell me more about how to do this 12v coil conversion??? or atleast temporaryly till i can sort the problem.
thanks
rob

You would need to buy a new 12v non ballast coil, then run a new wire from the fuse box ignition live to the positive on the coil.
But it sounds like only thing wrong with your existing setup is it appears the byepass wire described by Ethel isn't working.

[Wil_h]

Interesting. When you measure the voltage when not cranking it will be as you say around 6 V. Try measuring the voltage on the coil supply with the supply disconnected from the coil.

also, check the battery voltage when cranking, as it may be duff.

[dklawson]

I'm sorry but this comes up VERY frequently and there are some points I want to make as an extension of the suggestion above.

The ballast resistor (or resistor wire) ONLY drops the coil operating voltage to the coil when current is flowing. Period. That means to effectively measure the voltage drop, the points MUST be closed.

If you want to measure coil voltage the easiest way is to remove the distributor cap, place a coin between the points, then switch on the ignition. This insures that current will be flowing. You will then be able to measure between earth and the coil (+) terminal. A "standard" ignition will measure battery voltage on coil (+). A "ballast coil" will measure somewhere between 6V and 9V on coil (+). Don't forget to remove the coin before you refit the distributor cap.

As above, I agree that there must be something wrong with the white/yellow wire. As suggested above, measure the voltage between the starter motor side of the solenoid and earth when cranking... then repeat your test between earth and coil (+) when cranking. They should be the same value.