Cycle Up Lead Wire ??!!

[hansen12]

Hey Folks,
I've got a blue wire next to the coil of my '85 280i (US). It is marked with a factory sticker saying CYCLE UP LEAD. It isn't connected to anything and it's not shown in the bible. What is it?
Thanks
Rick

[iainjones]

Sounds like the ballast resistor, is it quite thick (maybe a little less than 1/4" dia), with bullet connectors, and wound into a coil about 4 turns at 4in diameter?

Regards
Iain

[hansen12]

Yes Iain,
It is a thick blue wire with an unused butt connector on it. It is one of the wires wrapped in the harness leading from the coil. What is its purpose?
Cheers
Rick

[iainjones]

I've never quite understood ballast resistors...but i think it goes a bit like this...

Ignition coils work at a set low tension (LT) voltage, eg 8volts. Normally the electricity going to the coil goes thru the resistor reducing the voltage reaching the resistor…however during start up the start relay bypasses the resistor feeding the coil 12v, except for the fact the engine is cranking so the system voltage could be as low as 8v, hence you can still get a spark during cranking…I think there is some logic to that…

Anyway from memory it should be connected to a connector with two yellow and black cables in it, one going to the starter motor and the other to the coil, the other end of the resistor goes to somewhere need the fuse & relay board…its on the wiring diagrams in the ‘bible’ if want to check

Edited to add

Having said that if my logic holds true the car wouldnt run without the ballast resistor connected...

>> Edited by iainjones on Thursday 28th October 12:28