Technical Electrical (ignition?) question

[S854]

Got my carbs cleaned up and reinstalled, as I was watching for fuel leaks on and under the carbs I noticed a "red box" which was very hot.... so hot I couldn't place my finger on it... I had the ignition on, engine off (I was running the electric fuel pump in the trunk).

You're going to have to talk to me like I'm a third grader... I know very little about electrical issues, or the components involved.

This box is attached to the coil via a bracket, with a green wire running to the distributer, red wire to one post on the coil. There's also a brown wire pigtailed to the green, the brown wire disappears into the wiring harness.

After turning the ignition off, the box cooled down rather quickly.

One more, possibly related item... as I was checking the green wire quick-connect (with the ignition off) I noticed the #4 plug lead wasn't securely fastened in its port in the distributer cap...

Is this box supposed to heat up, possibly not quite as hot with the engine running?

 

[124BC1]

That 'red box' is a ballast resistor (ceramic type, 0.8 ohm) for the ignition coil - it's purpose is to reduce the voltage being supplied to the coil (your coil runs on less than 12 volts). It will get very hot with the ignition on, but engine not running and the contact breaker points in the distributor just happen to be closed. It shouldn't get as hot with the engine running.

It's not considered good practice to leave the ignition turned on for a lengthy period without the engine running -if you need to do so e.g. when running the fuel pump, it would be best to disconnect either the red lead between the coil and the ballast resistor or the lead that goes from the coil to the distributor (possibly at the quick disconnect if fitted) in order to prevent current flowing continuously through the coil primary windings to ground if the contact breaker points happen to be closed (this can cause overheating and possible damage to the ignition coil).

The brown wire that 'disappears into the wiring harness' is what feeds the dashboard tachometer/revcounter. (this gauge counts the number of ignition 'pulses' at this wire and converts this into equivalent needle movement in the gauge indicating the engine speed in rpm).

Number 4 plug being loose in it's distributor cap socket/port is afaik not related to the ballast resistor getting very hot but obviously needs to be made secure - if you suspect this plug lead may have been loose for some time, it would be advisable to check that there is no damage inside the plug lead socket/port on the dist. cap e.g. burning/electrical arcing marks on the brass contact and no tracking marks.

 

[S854]

Awesome! Gonna file that info away for possible future use… when I was younger, I recall others say not to sit with the ignition on/engine off for extended periods… when all cars had points type ignition… now I know why (which is the most important take-away from this discussion)

I’ll check the ballast resistor temp later today while the engine is warming up…

I’m thinking I dislodged the #4 lead when I removed the coil lead as the engine ran fine last time I drove the car… I wanted to get the lead out of the way whilst removing/installing the carbs… I’ll check inside the socket before firing her up… just in case…

Is the resistor considered a wear item? I’m putting together a “reverse voodoo”, spares package to carry in the trunk — plugs, points, condenser, fuel filter, fuses, etc. — should I carry a spare ballast resistor also?

Also… I’m curious… how long have you been involved with the 124’s? You have quite a wealth of knowledge regarding them and I know, from first-hand experience, the best teacher is experience…