What are the symptoms of a faulty ignition switch if it had an open or shorted circuit?...... Would it produce a weak spark, causing the engine to run rough and possibly backfire out the exhaust?

An ignition switch most often goes bad due to "high resistance connections." One or more terminals get "crusty" and start to arc. The arcing generates heats, which further corrodes the brass terminals causing more heat... etc. Eventually the terminals get hot enough to start melting the bakelight insulating base, then they get loose and flaky. Eventually they don't work at all, and you have an open connection.

The terminals that fail are the ones that carry the highest load, eith the power in, or the starter terminal.

While anything is possible, the most likely symptom of a failing ignition switch is that you have to wiggle and jiggle the key to get the motor to crank over.

Backfiring and running rough are most often cause by problems with the distributor or sparkplug wires. I'd check the wires for burnthrough's near the headers, check the inside of the distributor cap for carbon tracking, the underside of the rotor for burn-through, stuff like that. Check the plugs, too, as well as the timing.

I'm trying to look beyond the motor and figure out what outside sources such as the ignition switch or perhaps the ballast resistor would cause running rough and backfiring out the exhaust.....The distributor, plugs and wires are new....My car is still at the shop, after 1 month and $1500, they said it was done and quickly wanted to tow it home, free of charge!.....I told them that I need to check the car out before you release it and it ran exactly the same as when I first towed it to them!.....They adjusted the valve lash, rebuilt the Edelbrock carb and installed a new Edelbrock "Performer" intake.....The engine is pulling 8-10 inches of vacuum and timing is set at 14 degrees.....They insist it's the carb so they're checking it out......I might add, the engine ran excellent the last 2 years!.....I told them I want my original intake put back on because I'm not paying for something it wasn't!.....If they refuse then I'll contact my credit card company and dispute this charge!.....This ignition switch is one of those $12.95 reproductions from NPD and I'm just wondering if that's the problem, it does crank and start good, it's just that after running a few minutes, it starts loading up, running rich and running rough then starts backfiring out the exhaust!

badbird i see you replaced the dizzy.is it hei or is it a point set up in dizzy.if it is a hei, you need to take the resister wire out and have a full 12 volts running to the dizzy.

Negative on the HEI.....It's a Mallory, double duallie!:yes:

What are the symptoms of a faulty ignition switch if it had an open or shorted circuit?...... Would it produce a weak spark, causing the engine to run rough and possibly backfire out the exhaust?

My Symptons:
No specific pattern to it, it doesn't happen with more left then right turns, bumps in the road make no difference..... the car will just dies. The dash indicators looked like you just turned the key to the run position before starting it. I wiggled the key and it fires back up. I inspected the wires and everything looks fine. I am convinced it is in the switch. Will change it out when the weather cools down, to hot to even take the car out.

the most likely symptom of a failing ignition switch is that you have to wiggle and jiggle the key .

I wiggled the key and it fires back up. .

Change the switch

I'm running a brand new Mallory Dual Point with vacuum advance, a Mallory "Promaster" coil along with the supplied ballast resistor.....The coil and resistor are not new however but were performing good for the last 2 years......Can a voltage test be performed on both sides of ballast resistor to determine what voltage the coil is receiving?.....What should the voltage be on the ignition switch side of ballast resistor and also the positve coil side of resistor?.....How can the ignition system be tested for a low or weak spark output?

Change the switch

When it stops being 100 Degrees.......... to hot to work on anything.

The point being that it is entirely unlikely that the switch is causing BADBIRD's problem. To convince yourself it is not the switch or wiring from the switch to the coil, I would rig up a voltmeter and monitor the voltage going to the coil. If the voltage dies down and the rough idle etc occurs start trouble shooting from the coil back. the resistor could be opening when getting hot. If the voltage stays up then follow Jim's suggestions.

When it stops being 100 Degrees.......... to hot to work on anything.

The point being that it is entirely unlikely that the switch is causing BADBIRD's problem. To convince yourself it is not the switch or wiring from the switch to the coil, I would rig up a voltmeter and monitor the voltage going to the coil. If the voltage dies down and the rough idle etc occurs start trouble shooting from the coil back. the resistor could be opening when getting hot. If the voltage stays up then follow Jim's suggestions.


Jim.....Jim's suggestion was to "wiggle and giggle the key to get the motor to crank over".....I have NO cranking problem, it starts fine, I have a running problem!.....If you read my follow up post, it covered his other suggestions.....So in other words, you're saying that a "hot", open ballast resistor could cause low voltage resulting in a weak spark, a rough engine idle and backfiring:confused:

The voltage at the coil should be somewhere around 7-9 volts. From an electronic stand point when a resistor starts to open (go bad) depending on how it is in a circuit will either change current flow or voltage level (For the electronic experts..KISS, I am not going to go into OHM's law). So, in theory if the voltage going to the coil is to low many of the symptoms you describe could be the results. If I had points in my car I could prove this theory.

just out of curiosity, have you checked to connections at the junction block behind the battery? Also at the horn relay?
I had a bad connection at the junction block when I first bought my car (a long time ago). Occasionally when I went over a bump, everything would die for a split second and then power would be restored. The engine would crank right back up with the key. The small lead from the pos batt cable should lead over to the junction block. the main fuse harness is tied in there too.
Those old blocks get rusty, break, wires come loose, previous owners make bad connections.... just a thought.

just out of curiosity, have you checked to connections at the junction block behind the battery? Also at the horn relay?
I had a bad connection at the junction block when I first bought my car (a long time ago). Occasionally when I went over a bump, everything would die for a split second and then power would be restored. The engine would crank right back up with the key. The small lead from the pos batt cable should lead over to the junction block. the main fuse harness is tied in there too.
Those old blocks get rusty, break, wires come loose, previous owners make bad connections.... just a thought.


Steve....This car has been completely rewired with the 18 circuit, Painless Wiring kit.

A couple other things I notice is the alternator gets extremely hot to the touch after a few minutes of running, with a fully charged battery!!.....Also, I notice that the external voltage regulator makes a momentary "clicking" noise when you switch the key to the "on" position!.....Both of these components are new also!.....Would or could these problems be related to the ignition problem?

The voltage at the coil should be somewhere around 7-9 volts...

Beware that with a breaker point ignition, the voltage will be anywhere from 12 volts (full system voltage rather) to something less than 7-9 volts. The 7-9 volt figure comes from a running motor where the breaker points are toggling on and off. Don't measure this voltage with your fancy digital volt ohm meter. Use an analog volt meter. A DVM can easily be damaged by the flyback voltage present on the coil (+) terminal.

I filed a complaint with the Department of State, Bureau of Automotive Regulations, against this so called repair shop!....They completely misdiagnosed my engine problem and charged me $1500 for just adjusting valve lash, which it didn't need, taking off my single plane and installing a dual plane intake manifold, which it didn't need, and rebuilding the carburetor, which they botched up, the throttles don't even open to WOT!....There was nothing wrong with the carb to begin with and it never needed a rebuild!.....They towed the car back and the first thing I did was installed a new ignition switch which was the culprit all along!.....Apparently low voltage was causing weak spark output and all the problems!.....These so called mechanics, in their mind, still think the camshaft is causing the problems and wanted to tear down the motor and check it out!.....I won't be happy till I get every bit of that $1500!.....The case is under investigation as we speak.