Thread: what's this please?

That appears to be some type of 'ballast' device, cheers Dennis

The purpose of the "ballast resistor" is to provide a reduced current to the ignition coil while running. The ignition coil should have "USE WITH RESISTOR" stamped on it otherwise it is probably the wrong one. When the starter motor is operated an extra wire usually cuts the ballast resistor out of the circuit so that all remaining battery voltage gets fed straight to the coil.

Depending on the vehicle and the amount of fiddling done by previous "mechanics", this function may not be present leading to hard starting when cold. It is easy to make this function work by either a relay or direct feed from a special terminal on the starter or the key switch.

Beautiful thanks.
I'll go see if there's anything stamped on the coil + check out where all the wires go.
cheers,
D

I had a new coil on the list at some point so may as well change the resistor as well which looks like its about to fall apart. I'll see if I can see anything heading off to the starter motor.
cheers,
D

Take a look at the starter solenoid and see if it has an extra spade terminal on the side, other than the one that operates the starter motor. It would be wired directly to coil +.

Modern ballast resistors (along with nearly everything auto electrical made now) are almost universally crud, with thin tin plated steel terminals that rust and fail within months. The best made ballast resistors were fitted to 1970's Datsuns, such as 120Y and 180B models. They almost never failed. I used to undo one of the clamp screws and reduce the length of the resistor wire to increase the power for Bosch GT40R coils. Haven't seen one in donkeys years though.

Originally Posted by bee utey

Take a look at the starter solenoid and see if it has an extra spade terminal on the side, other than the one that operates the starter motor. It would be wired directly to coil +.

To be clear, its an extra terminal that's not a double off of the terminal used to kick the starter solenoid in.

The terminal you're looking for should be on the opposite side to the signal terminal and will not be live while the solenoid is not engaged.

Its starter dog and ring gear destroying when someone hooks up the coil + to a doubled spade on the starter signal wire.

OK - I'm kind of there I think.

Pic shows ins and outs of the Solenoid minus a wire out of shot off the nut terminal on the left which goes to the Alternator. R/H nut goes to Starter. Small Red and White wire and thick Brown wire head off toward the dash.

I'm guessing the spade terminal opposite the terminal with the red and white wire is what would take the 12v supply to coil + if it was there. As its not there , I'm assuming the coil is only getting 10 volts at start up - but its always started fine from cold , no trouble.

What is the point of the Ballast resistor? Why would you want less volts when running - is it to prolong the life of the Coil? I'd say it works judging by the date on mine. If I ditch it - would I notice?
cheers,
D

Connect a light bulb to your new found terminal and see of it lights up during cranking. Make sure the terminal isn't internally connected to the start terminal when not actually cranking. The ballast resistor exists because some days your battery may not be at 100% and sometimes there is a deep frost on the bonnet. If your starter motor bearings get a bit dry it will draw a higher current, reducing the voltage for sparks. Connecting the ballast resistor cutout wire will not harm the vehicle.

If you just remove the resistor your coil will probably overheat and explode. That is why it is clearly marked "use with resistor", they wouldn't bother if it wasn't important. Before the days of giant warning stickers and the obsessive nanny state things like that were just written without further commentary! A straight 12V coil must be used instead if you remove the ballast resistor.