Ignition switch problem?

[Tom L.]

Good evening all, Happy 4th!! Anhyway, Have been having a problem starting my '72 LS-5 Automatic for a while. A while back the car just didn't start one day. The battery was 6 years old and tested marginal, and the starter that was in the car has been in there for the 17 years I've owned it and it was of unknown origin. I had bought a rebuilt correct starter a while back so I put it in and put a new battery in. I figured that that would solve the problem.

Once installed it started but not reliably. After messing with it, I found that if I jumped from the battery cable connection on the starter to the start terminal it would quickly, without hesitation engage and turn the engine over. While checking I found that I only had 8 volts at the start terminal on the starter when cranking. After messing with it for a while it seemed OK so I let it be. Took a couple of rides and all seemed OK.

Last week I went for a run, when cold it started just fine. No issues. Had lunch after an hour of driving and after sitting when I tried to start it and the solenoid chattered but the engine did start. Off I went and let it be, that was a mistake.

Today Basically the same scenario, drove an hour, had lunch and went to start the car. Nothing... So... I let it rest a while with the hood open to let it cool. After about 45 min. it reluctantly started but with the same chattering as the last time. Got home, all is OK

Here's what I'm thnking. From the ignition switch to the starter there are no splices or additional connections to the start terminal from the ignition switch according to the wiring diagrams I have. So what do you think, Ignition switch???

Thanks!!

[Owen L.]

Re: Ignition switch problem?

Could this be an instance of voltage drop?
Someone with more experience testing for this can tell you how to set up a multimeter to see it.

[Tom L.]

Re: Ignition switch problem?

Definately thinking voltage drop. Just not sure ehat the test points would be BEFORE the ignition switch and between the ignition switch and the starter.

[Richard M.]

Re: Ignition switch problem?

I'd pull the ign coil wire(so it doesn't run), put a voltmeter on the Violet wire terminal at Solenoid S.

Crank engine for 5 seconds and record the voltage on meter.it should be around 11 to 12 volts or better.

I don't have a 70-72 wiring diagram handy, but doesn't the violet crank wire go from that hidden Ign Switch on the column through that big bulkhead connector at the driver side firewall?

If it does, I'd inspect that first before thinking of replacing the switch.

Rich

[Daniel S.]

Re: Ignition switch problem?

What is the condition of your battery cables? The black/ground needs a good solid connection to the frame located just outside of the battery tray.
Space is tight where the positive runs around the passenger exhaust. On my L71, the shielding had melted due to the close proximity to the exhaust and the metal strands had begun to corrode. This sort of situation can affect how many amps make it to the starter.

[Richard M.]

Re: Ignition switch problem?

Agree that the negative cable to the frame could be suspect.

If that's there....
I went to my '69 Aim and shows that purple Sol S wire goes from Ign Switch, through a connector, and the Bulkhead connector. Also through neutral safety switch.

If any one of those connections is faulted then it would create a corroded condition with voltage drop. There are apx 8-12 amps running through that circuit during CRANK, and could be higher at elevated temperature.

20240705_134640.jpg

Screenshot_20240705_133752_Gallery.jpg Screenshot_20240705_133539_Gallery.jpg

[Bill B.]

Re: Ignition switch problem?

Tom I had a similar issues years ago. Mine turned out to be the clutch safety switch dropping excessive voltage. Would always crank when cold, but not budge when hot. The clutch safety switch is in series with the solenoid coil, so when the solenoid was warm the marginal current flowing thru the switch and solenoid would be insufficient to pull in the solenoid plunger to engage the starter.

You have an RPO M40 Automatic, so your equivalent of the clutch switch would be the Neutral Safety Switch. I'm not saying this is your root issue, but worth investigating as possible source of the voltage drop.

[Tom L.]

Re: Ignition switch problem?

Hi all, thanks for all the input. This thread sat because I traveled and came home to that darn 4 letter word... WORK. Anyway, I did get some time to spend on it last week. Did all the tests that were suggested along with some others and did find voltage drops at all points. Near the end of the process my wife, BEST helper ever, smelled burning plastic. I figured that something got hot (DUHH) so I just felt around and the hot spot was the positive connector on the battery. Very Hot. BTW, all this was done without any engine heat.

A week passed and I got back to it. I figured I'd just trim the wires at the battery 2 inches and get new battery terminals (Side post and they had been replaced before). When I cut the cables the negative was a modern #1 wire but the positive was the old crappy copper clad wire. I cleaned up the old wire by scraping it, put the new terminals on and gave it a whirl.

We cranked it for a while and everything worked as expected. Battery voltage was 12.5 at the start, 10v while cranking (for a while). No starter shatter and almost no heat at the positive terminal on the battery.

Next test is to get it started, go for a run without stopping and see if it restarts with engine heat. At home of course : )

Sooo... I'm thinking positive wire to the starter has just run it's cuorse, just too old.

Thoughts?

[Mark E.]

Re: Ignition switch problem?

It makes sense the problem could be battery cables/connections with high resistance. Low voltage at the starter end of the cable was a big clue.

I suggest repairing it properly with new cables. Clamp on terminals cause resistance and promote corrosion, and are not a good long term fix.

Make sure the connection of the negative cable to the frame is clean and tight. That's a common source of resistance too.