Distributor/coil wiring

[furnitureguy-123]

I am confused,(as usual), right now my distributor lead is hooked to the positive terminal on
the coil. Is this correct? Should the dist. be hooked to the negative? The truck has been running fine, I just noticed it when I went to change the points. I can't tell from the wiring diag which way it should be.
1966 F100 stepside w/1980 300-6

[seattle67]

Yup, distributor should go to the negative terminal on your coil.

[m-mman]

The circuit design is that the key sends power to the "positive" side of the coil, the power travels through the coil then out the other (negative) terminal then on to the distributor and then to the points where it is grounded. It is the intermitient grounding of the points opening & closing that creates the high voltage spark.

To "hot wire" a car in the old days was to run a jumper wire to the positive side of the coil (just like the key does) then crank the engine at the solenoid and it starts so you can steal it away.

To defeat this tactict an owner ran a wire from the negative side of the coil to a hidden switch in the interior, then to ground. When you left your car you hit the switch and grounded the coil which prevented any sparking. Hopefully the theives would find out the car wouldnt start and go elsewhere.

This was the famous 'kill switch' that many a home mechanic beleived that they invented and nobody else had ever heard of it.

[furnitureguy-123]

Thanks! Based on m-mmans description of the circuit, I am not sure how the thing was running!!!! I did make the switch and i did not notice much of a difference in the way it runs.
At least I know it is wired right.. Thanks again!

[rjewkes]

i beleive it still worked because it is a pass through.

[ToughOldFord]

It'll work, fine usually, but you'll burn points up pretty quick.

[m-mman]

The points type ignition system was very simple and robust which is why it was used for so long. If your coil was wired backwards it does still produce a spark, but not as efficiently and can result in low voltage sparks at high RPMs and in high heat situations. (which you may never notice if you never stress your truck)

I feel compelled to remind you to just verify that your battery was also installed correctly. (negative ground) If your coil AND battery were BOTH backwards, then it was all still working well because at that point the ignition system was actually wired 'correctly' with both backwards. (yeah, strange I know)

Here is the story where I learned,
I worked on a friend's 1959 Edsel once, it had multiple problems but still ran. As I was tinkering with a bunch of things under the hood I suddenly noticed that the battery had been installed backwards(?) [installed as a Positive ground]

I couldnt believe what I was seeing because I never really saw anybody do this before. Turns out some idiot put it in that way because they had been told that "All old cars are positive ground". (back in the 6 volt days, they were)

So I simply turned the battery around (negative ground).
The car had run OK with the battery installed both ways but then suddenly it wouldnt run at all over an idle(?)

Everytime you reved it up it was as if you were pouring gas down the carb (serious bogging down, zero power, wanted to stall) But it would idle perfectly.

Turns out when the battery was backwards it burned out the condenser because it was charging the primary side of the coil and running high voltage into the condenser.

All this resulted in a VERY MINIMAL spark plug voltage. The spark voltage was so low that it was being 'blown out' at high RPM. (anything above idle) After hours of checking EVERYTHING else, I finally swapped the condenser (how often do those things fail?) and everything was perfect. It is still running perfect, no further problems.