Classic Car Electrical problem

So, my 1970 Road Runner (440 automatic) started fine last week. Today it would not. It’s turning over, but sounds like it is not sparking. Also, when I stop cranking it, but leave the key on, there is a buzzing noise coming from near the coil and distributor. I put on a new coil, but no luck and still a buzzing sound. Any ideas?

Have you checked the points inside the distributor? How about the condenser? Do you have a dwell meter? Do you have a volt meter?

Does it seem to catch when cranking but just dies when you release the key to the run position?

No, I haven’t checked the points or condenser yet. It’s the buzzing noise that’s confusing me…

The buzzing is probably the dropping resistor vibrating. Its a wire wound resistor and they tend to do that. It might also be the voltage regulator trying to keep from burning up the field coil in the alternator. The voltage regulator is mechanical. It is a relay that might be cycling on and off real fast.

Please answer all my questions above at one time, it will be quicker this way.

I plan to check all. The ballast resistor is on the firewall. The buzzing is in the front of the engine bay around the coil/distributor area. Would a faulty resistor make the coil buzz? The the car sounds like it is cranking normally, just not starting and has the buzzing noise up front.

I wouldn’t worry about the buzzing, check your points.

jump across this resistor on the fire wall, and see if it starts.
If it does, replace the resistor.


1 Like

Will do…Thanks.


Last post tonight. If the points are burned and not conducting, then the coil and the condenser which form a tuned circuit, will be energized and resonate. Being that the coil is so big, it might resonate at a low frequency. Now you cannot hear the electromagnetic fields vibrating, but nearby small metal parts will react to the changing magnetic fields and vibrate. If the resonance is within the human audio range, you would hear that as a buzzing.

1 Like

What Yosemite posted a link to is commonly called a ballast resistor. In the 60s, 70s and 80s My wife, children and I were all driving Chrysler corp cars for the most part. There was a spare ballast resistor in the glove box of every one. Helped a lot of people broke down on the road. The used to cost $1.50 back in the day/

1 Like

Ballast resistor, that was the term I was trying to remember. @Yosemite did not recommend replacing the resistor but gave a procedure to test it. I support doing that test. If it starts, then replace the ballast resistor or you will be replacing a lot of coils instead.

If the condenser is bad, doesn’t that allow a spark the jump across the points? Maybe that’s what you’re hearing.

Check points and condenser. Usually we just replaced condensers if any question.

@keith I did recommend replacing the resistor , if jumping it allowed the car to start.

@oldtimer-11 . We too kept a spare in the glove box.
They were cheap then, but so was everything compared to the prices today.
We’re showing our age!!!

My understanding is that, when the auto industry went from 6 volt to 12 volt…Chrysler Corp decided to change over to 12 volt,but keep the 6 volt ignition system to save on changeover costs. Thus the resistor.
You can run the system on straight 12 volt for a short period, but as @keith says you will be replacing the coil or at the least burning the points up.

For anyone jumping the resistor…as I suggested…This is only for testing purposes, or a short trip to town for a new resistor.Replace it ASAP if jumping it, allows the engine to start.


When key is in the START position, the ballast resistor is bypassed so the car will start, but immediately stop when the key is released to the RUN position if ballast is bad.

I know what you meant, I just didn’t say what I really meant, which was that you recommended testing before replacement. I agreed with you 100%.

If you kept a spare in the glovebox it was faster and easier to just unplug one and plug in the new one. it would work even if just dangling by the wires if you didn’t have a wrench with you.

You might pop the distributor cap loose and watch the rotor as you crank the engine over.

If the rotor is not turning it’s quite possible the offset tang on the distributor drive has broken off. That is not a rare thing to happen.
Many distributors have a driven gear on them. Not the Mopars of this vintage. They have a flat tang.

I got off work one evening and my '69 Superbee would not even cough. The tang had decided to shear off. Luckily there was a salvage a 1/4 mile down the road so a 25 dollar distributor got me rolling again.

@ok4450 Did you get the broken tang out with a magnet.


Recon the OP has figured it out yet?