Bad Ignition Switch? - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 7 (permalink) Old 09-26-2018, 09:26 PM Thread Starter
Join Date: Oct 2015
Location: West Chester, Ohio
Posts: 15
Bad Ignition Switch?

I've got a 1967 Impala that quit running while driving today. I've run into a problem with a short in/near the ignition switch that prevented it from starting before. If I reach under the dash and apply a little pressure to the wires, it would start up. Similarly this time, I applied a little pressure, started it and I was on the road. But it happened a couple more times and the final time I could not resolve it. Car would crank but not start.

I thought it was a splice that spliced in an electronic distributor via a wire through the firewall into the ignition. I replaced that splice, tested continuity and confirmed that I am definitely getting current to the distributor when I turn the key on.

The issue is either in a wire on the small plastic "harness" that connects to the ignition switch or the switch itself. Do those switches go out often? Is there any way to troubleshoot this? Any other thoughts?

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post #2 of 7 (permalink) Old 09-27-2018, 05:47 AM
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Location: Greenville, SC
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Is it HEI? If so, check the ignition module. Always the first thing to go in an HEI distributor.

1968 Impala SS
496 Stroker
T56 Conversion
3.73 Posi-Trac
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post #3 of 7 (permalink) Old 09-27-2018, 07:08 AM Thread Starter
Join Date: Oct 2015
Location: West Chester, Ohio
Posts: 15
Yeah, it's HEI. But I'm still inclined to believe it's a short at the ignition switch itself since yesterday I was able to jiggle the wires and get it to start. But I will look at continuity at the ignition module. Thanks.
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post #4 of 7 (permalink) Old 09-27-2018, 10:12 AM Thread Starter
Join Date: Oct 2015
Location: West Chester, Ohio
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This morning I pulled the ignition cylinder out. Checked all the connections, put it back in and cranked with still same results. I checked continuity at the coil again and this time had no power with the key on.

I pulled the ignition out again, bridged the ignition switch harness between the battery + and ignition with a small wire. Tested continuity at the coil and I did have power.

Seems to me the ignition switch is funky. I am picking up a new one today and will install and report the results.

What's up with this funky light attached to the ignition switch barrel thread? It goes up to a position behind the clock. Seems like a strange configuration.

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post #5 of 7 (permalink) Old 09-27-2018, 10:18 AM
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Switches wear out as the contact points both burn and abrade with use. The housing that supports the barrel that turns also wears allowing misalignment that further causes the points to burn. Finally the wires where coated with the earliest application of PCV plastic that cracks and falls off with age as it becomes brittle from heat (replacing silk cover cloth insulation).

That light was a rare option (for a Chevy, standard equipment on a Cadillac) that illuminated the bezel of the ignition switch.

The HEI module is composed of transistors that do not like changes in voltage such as power being cut off and on while running.

So it could be two problems one caused by the other.

Even in the sixties the price of virgin copper was rising as all of the easily available mines had played out thanks to WWII. Because GM is run by bean counters, it always used the minimum diameter wire (gauge) and cut it to the minimum length. As such I always ripped out factory wiring and replaced it with the minimal circuits that were needed in a race car using a heavier gauge wire. This reduced weight and improved reliability. Ignition switch was replaced with a toggle switch (on-off) and a momentary contact switch (push button start back in the sixties). Those two switches were lighter than the ignition switch and the housing with shiny trim bezel.

On my daily drivers such as my Suburban with 370,000 miles on the odometer I had to replace the ignition switch twice as I wore it out (three times as I had to replace the steering column once as it fell apart from wear and bought another switch to get a key to operate the truck).

Big Dave
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post #6 of 7 (permalink) Old 09-27-2018, 09:33 PM Thread Starter
Join Date: Oct 2015
Location: West Chester, Ohio
Posts: 15
Interesting info Big Dave. Definitely was a combination of multiple things. I believe the light that is attached as shown is in fact the GEN idiot light. I know the light you speak of. I've fiddled with it in the past when I was messing with gear alignment on the indicator. I've had a heck of a time with the ground on that one. But it connects into a different location on my '67.

68WASAGOODYEAR, you were right on. After replacing the ignition switch, rotor, and distributor cap, I eventually made my way to the ignition control module. My hunch is that it was originally a short at the ignition, sending a bad connection to the distributor, eventually fouling that module. Sounds like it doesn't take much from what I gather.

Thanks for your input. I'm back on the road!
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post #7 of 7 (permalink) Old 09-28-2018, 09:31 AM
Join Date: Jan 2006
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Transistors are fragile animals. It doesn't take much of a voltage spike or heat rise to kill one. For this reason the military has their own grade of transistors. Those that fail to meet Mil Spec are moved down to premium grade, and those that fail that QC check for premium are sold as consumer grade transistors. Because the price falls with the reduction in quality and reliability the choice of what to buy is economic. You would never guess which grade GM buys for it's electronics, but since bean counters make the decision I guess you know already.

This is one of the many reasons why you pay more for a MSD HEI distributor, than a stock one out of the bone yard (brass instead of aluminum contacts, larger centerless ground shaft sitting in a forged billet aluminum housing with a big heat sink under the HEI module are others). MSD used to use Mil-Spec transistors in their American made HEI units (not so sure what is in them now since they moved manufacturing off shore to China to make more money for the investors). The ones I bought twenty five years ago are still going strong.

Big Dave
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