Help, ballast resistor 1948 Pontiac

Car has not been started for 9 years. Note: Converted to 12 volt battery a nd 12 volt ignition coil 15 years ago and run as daily driver until parked.

Tried to fire it up and no spark. Messed around for hours, tried 3 differe nt coils, etc. to no avail. Finally, upon bypassing the ballast resistor I got a healthy spark and car started immediately. (yes, with 9 year old gas oline)!

The resistor (original, I believe) is installed in the negative side of the coil. It goes from the distributor ground to the negative terminal of the coil. The resistor measures approximately 2 ohms, has continuity and is e xtremely hot after cranking the engine for about 5-10 seconds.

As I said, absolutely no spark with resistor in place, but healthy spark wh en bypassed.

Question: Can't find any diagrams with resistor in the ground circuit of t he coil. All diagrams show resistor wired in the hot circuit between the i gnition switch and the positive side of the coil.

Please note that this car was a daily driver nine years ago and nothing has been touched or re-wired since that time. Can't find listing for ballasts at Rockauto and other internet sites.

Thanks you for your attention,

Ivan Vegvary

Reply to
Ivan Vegvary
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Does it stay running if you remove the bypass after it starts? I don't know about a 1948, but most cars had a resistor on the positive side, but there was a bypass circuit when cranking. The ones I'm familiar with had the bypass coming off of the starter solenoid or relay, but I suppose it can be done with the ignition switch too.

Reply to
Bill Vanek

Thanks for your reply Bill. Car runs fine without resistor. Very simple circuit. One hot wire to coil (through ignition key). One wire from negative of coil to points. This negative wire has the ballast resistor in series. By the way, starting is done through a mechanical push with your right toe to engage the starter pinion with the ring gear. Thanks Ivan Vegvary

Reply to
Ivan Vegvary

Sounds like it was wired wrong in the conversion. The common method for wiring would be points grounded, condenser case grounded, movable contact on point connected to wire&condenser lead. Wire from those to negative side of coil. Positive side of coil to ignition switch.

No ballast resistor was/is needed with the original 6 volt system.

When GM switch to 12 volt they actually didn't change the ignition system much. Still a 6 volt coil on most engines right up until HEI came about. GM used a ballast resistor for less than a year. They used a resistor wire most of the time. The resistor was used to drop the voltage enough that it kept the coil cooler and the points lasted longer.

However to ensure easy starting during engine cranking GM (and others) used a bypass feed. This was for a simple reason. The ballast resistor drops the line voltage from 12 volts to around 6-7 depending on the charging system. However during cranking the starter (also a 6 volt motor for many years) drops the battery voltage quite a bit. So now you have maybe 8-9 volts while cranking, this gets cut in half by the ballast resistor and you get poor engine starting due to the very low voltage.

So if you do a 12 volt conversion you add a ballast resistor and a relay that is triggered while cranking only. The relay will feed full voltage around the ballast resistor to ensure the engine starts.

In your case the burned out resistor stopped all voltage.

This shows the original 6 volt ignition system.

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Full wiring diagram
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Reply to
Steve W.

and 12 volt ignition coil 15 years ago and run as daily driver until parke d.

rent coils, etc. to no avail. Finally, upon bypassing the ballast resistor I got a healthy spark and car started immediately. (yes, with 9 year old g asoline)!

he coil. It goes from the distributor ground to the negative terminal of t he coil. The resistor measures approximately 2 ohms, has continuity and is extremely hot after cranking the engine for about 5-10 seconds.

when bypassed.

the coil. All diagrams show resistor wired in the hot circuit between the ignition switch and the positive side of the coil.

as been touched or re-wired since that time. Can't find listing for ballas ts at Rockauto and other internet sites.

Wow!! Thanks Steve W.

That's the clearest answer I found even after several hours searching on th e web.

My coil is rated for 12 volts so I will simply skip the ballast resistor. BTW, if I were to install a new resistor (extremely inexpensive) I suspect that it should go on the positive (hot) side of the coil and NOT the way mi ne was wired. Thanks you again, Ivan Vegvary

Reply to
Ivan Vegvary

On most cars, the ignition switch should be applying power directly to the coil on the start setting, and through the ballast resistor on the run setting.

So, if the ballast resistor is open, the car will start but then as soon as you let go of the key and it moves to the run position you will lose spark and it will stall out.

So if you aren't getting spark on either run or start, but you DO get spark. on both with it bypassed, you have something unrelated going on.

NOW... I _think_ your car doesn't have that bypass, that the ballast resistor is always in circuit even during starting. You need to get the service manual and make sure that is the case.

Sounds like your coil is bad.

The fact that it gets hot would indicate that it's good and the connectors on it are good too.

Shouldn't really matter which side it's on, but you can rewire it to put it in the hot side if you prefer. I'd probably do that unless it's very clear that it was wired originally the other way.

I don't think the ballast is your problem, but you can probably use any other

6V ballast resistor off the generic rack.

I am assuming this car is as stock, that it hasn't been converted over to a 12V system, right?

--scott

Reply to
Scott Dorsey

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