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1968 GTO w/ 400. Eng and tranny have 9K miles. Last week after getting on the highway and having a little fun with her I stopped at a gas station. Came back out and nothing! A buddy jumped the car with no issues. The battery is brand new and reads ok. The car did fine for a week at normal driving conditions. I replaced the alternator just in case. Then yesterday after taking her on the highway and getting on her a little the same thing happened, but this time she won't even jump start! No sound at all with the key turn, WTH! Starter? Wiring harness? Short? I am a newbie, so go easy on me.
 

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Buy or borrow a remote starter switch, or jump the solenoid terminals with a screwdriver to see if it turns over. Make sure you are bridging the +12v "BAT" terminal to the "S" terminal on the solenoid. IIRC, the S terminal has the purple wire.

If it cranks with either of those methods, then you'll know the problem is in the ignition switch or starting circuit/harness. Could be a bad ignition switch, a flaky neutral safety switch or an open circuit in the starter solenoid circuit.
 

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Does it start okay after it sets and everything cools down? If so, it could be a "heat soak" issue with your starter. Just an idea.
 

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My '67 did that. Eventually went to a high torque mini starter and Nbr 2 gauge cables. No hot start issues since.
 

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9 times out of 10 it's high resistance in the purple 'S' wire from the ignition switch to the solenoid. If you can start it by jumping the S and Bat terminals on the solenoid, that's the problem for sure. I've run into this on MANY old Pontiacs. On my own '67, the "S" wire was bad right behind the ign. switch.
 

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Many good suggestion and most of which I have and would also try myself.

My experience with this seemed the solenoid on the starter would go bad. When younger, I didn't know what I know today about the heat shield that is available to protect the solenoid from the exhaust manifold heat. I ran my cars hard and the solenoid most likely got pretty hot at times and burned 'em up. I used to keep a spare solenoid in my trunk at all times, no matter what Pontiac I happen to have registered at the time. I got pretty good at dropping a starter in a parking lot, installing a new solenoid, bolting it back up, and going about my business in about 20-30 minutes.

If you turn your ignition key on, does the red generator light on the dash come on? It should. If not, then perhaps you are not getting power to the switch. If you get the "gen" light and no start, it could be the ignition switch, but don't decide quite yet before doing other checks.

Now it has been a while since I have done this, so somebody correct me if I am wrong, please. You could use a test light to make sure you have power at the starter solenoid at the 12V BAT terminal. Then put your test light on the "S" (purple wire) terminal. It should light up when you turn the ignition key all the way just as you would to start the engine. If test light lights up, but engine does not turn, my guess is it is the solenoid or the starter. If it does not light up, then it could be the contacts inside the ignition switch have gone bad (this happened on my Lemans -they do wear out), or the purple wire to the solenoid has issues.

Things that can pose a problem that can be checked, corroded battery cable, bad ground cable, solenoid, the starter itself, neutral safety switch on an automatic (try it in neutral & park and jiggle it to test -short of it gone flat bad), wires going to the solenoid as described, ignition switch gone bad. I am pretty familiar with jumping the solenoid terminals with a long screwdriver (could never afford a remote starter switch) as I had to do that a number of times as well. Was easy as I had no heat shield and stock manifolds.

Just do your checks step by step to eliminate/narrow down the problem. Get stumped, just post an update and let us know what you did or need to do.
 

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Jim, the problem with the test light is that it won't check for current...just voltage. Even if the resistance is very high in the S wire, the light will still illuminate, but nothing will happen at the solenoid because the current isn't available. I usually find that every time I replace the complete S wire from the switch to the solenoid, no heat shields, trick starters, or remote solenoids are needed for easy starting. It's simply a matter of 45-50 year old wiring building a lot of internal resistance and preventing current flow. That's why jumping the S and Bat terminals at the solenoid itself is a great way to determine if it's an S wire problem, battery wire or battery problem, or solenoid issue. I'm stating this because I've run into this a lot on these cars, and it always seems to be that pesky S wire.
 

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Jim, the problem with the test light is that it won't check for current...just voltage. Even if the resistance is very high in the S wire, the light will still illuminate, but nothing will happen at the solenoid because the current isn't available. I usually find that every time I replace the complete S wire from the switch to the solenoid, no heat shields, trick starters, or remote solenoids are needed for easy starting. It's simply a matter of 45-50 year old wiring building a lot of internal resistance and preventing current flow. That's why jumping the S and Bat terminals at the solenoid itself is a great way to determine if it's an S wire problem, battery wire or battery problem, or solenoid issue. I'm stating this because I've run into this a lot on these cars, and it always seems to be that pesky S wire.

OK, I can agree with that. If corrosion or something of that nature affected the wire then there would be voltage flow, but not the needed current flow -there would be resistance. I have used an Ohm meter on occasion and again, been a while in using one, recall this would show the current flow (voltage) or drop in current flow? I hate electrical/wiring problems. HaHaHa.
 

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Great suggestions on the wiring, but that's not the whole picture. Remember that inside the end cap of the solonoid is the copper post which contacts a copper disk. The contact point of these two items becomes a source of high resistance due to the repeated arcing over time. This can be remedied as a free fix by taking it apart and removing and rotating the post 180 degrees and flipping the copper disk over. This gives two new, clean contact surfaces.

I've done this numerous times and saved myself and other alot of aggravation and $$ over the years.
 

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Great stuff. Jim, you need to use a real voltmeter/ammeter to check for voltage drop and current flow accurately. I've tested the resistance of a battery cable with an ohmmeter, it tested ok, but wouldn't carry current (amperage).....turned out, only 2 of the 18 or so strands of copper were actually intact. So it ohmed out ok, and lit the test light, but would NOT power up the starter motor. I too, HATE electrical problems. I am a mechanical/visual guy, not an electrical/theretical guy.
 
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