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A few months back I left my ignition in the accessories position overnight and discovered the car was dead; no lights, no power at the ignition, nothing. The battery has 12 volts. Thinking I had fried my ignition switch I replaced it, but that was not the problem. How does the power flow to the ignition switch and what should I test to track the issue? Thanks.

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if the batterie is fully discharged it is often impossible to "reactivate" it per modern electronic charger, as the charger does not recognize it. Sometimes a standard Power supply helps to "wake it up", then switch to modern charger.

I killed by same mistake one of this famous RED Batteries a loss of  >100$.


The battery is 12.5. With a charger it is indicating  >14. The car also has a Sniper FI which is separately wired to the battery and indicates the same as the VOM. There is no power at the ignition switch or the fusebox.

Before the car is started how does power flow to the ignition switch and fuse box? From the battery I see the big starter wire, and also one wire that comes through the firewall and disappears in the harness. Thanks

"Before the car is started how does power flow to the ignition switch and fuse box? From the battery I see the big starter wire, and also one wire that comes through the firewall and disappears in the harness."

9EF369BC-10D8-43A8-A8F4-065D01218F9A_1_201_aThe source of power to the wiring harness and fuse box is the 8 gauge or 1/4 inch wire on the back of the alternator.  It goes into the harness and goes all the way to the amp meter in the front console, then back to fuse panel, and all the way back to the starter solenoid in the engine bay.  That is where power to charge the battery happens.  Essentially, leftover power that is not used up along the way goes to charge the battery.

You could have corrosion or bad connections at the amp meter or at the starter solenoid.  I have had a problem at both of these spots.  In my case they manifested as smoke.  Also check the connection of the battery ground cable in front trunk where it bolts to the chassis.  It can get corroded and I have seen it get hot and smoke as well.

Finally, there is a critical ground inside the dash.  It is behind the speedo or tach.  If that gets corroded and stops working as a ground then not much on the car's electrical system will work.


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  • 9EF369BC-10D8-43A8-A8F4-065D01218F9A_1_201_a
Last edited by stevebuchanan

"Before the car is started how does power flow to the ignition switch and fuse box? From the battery I see the big starter wire, and also one wire that comes through the firewall and disappears in the harness."

The description I wrote above is when the car is running and thus I did not address your question.  Before it starts the source of power is from the battery through the 1/4 inch wire that connects at the solenoid.  Power is moving the opposite direction of when the car is running.  The amp meter shows negative amounts when the car is on but not running.

(Referring to 6/15/72 wiring Diagram)

To clarify the power from the battery, there are two black wires from the battery - one is the large wire running to the starter solenoid. The other is going to the ammeter. Then a black wire comes out of the ammeter and has a junction (well hidden in the harness) where, in essence, 4 pink wires are connected, two going to the fuse box #7 (30) amp & #8 (15) amp. With the other two pink wires, one goes to the headlight switch, and the other goes to the ignition switch. These wires are hot and power fuses or switches

The Power Distribution diagram above outlines the "P" (Pink wires).

Personally, I eliminated my ammeter and installed a voltmeter. There are a number of posts regarding possible problems with an ammeter, which may be the source of your problem.

An update. I had Autozone test the battery and they said it is healthy. 94% charge and 12.4v.

The ammeter isn’t an issue as it was already deleted. The battery and alternator wire are bolted together.  

Now this will sound odd but take it with a grain of salt from someone who doesn’t know auto electronics.  It seems like the polarity in the car is wrong, or the car is ungrounded. I tried testing the power wire coming from the battery to the where it was bolted to the wire from alternator and nothing. I took a power probe to one of the switches and gave it ground and power came to the car; the courtesy light came on and the electronic fuel pump came on. Thoughts?

Steve also mentioned the cleaning the connections at the harness ground stud in a prior post.

It's located sort of behind the tach, a little above center on the left side of the photo. The round tube is the cowl vent drain.

You mentioned you'd changed the ignition switch too? Maybe recheck the connections/retighten the set screws in the flat four wire connector that joins the switch to the car wiring?


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Last edited by larryw

Thanks, everyone for helping me troubleshoot.

John. I definitely used the power probe to supply ground, not the power, and that is when the car came alive.  I also dug into the console yesterday and tested the ammeter connections with the VOM and there was no reading with the positive probe on the wire and the negative on multiple places on the chasis.

Later today I am going to do the usual backflip contortion thing and check the ground under the dash as well make sure the negative connection in the trunk is corrosion free so I can continue the process of elimination.

Have you tried probing from the battery positive post to the ground stud in the front trunk?  

On the '72 and later cars, the battery positive post has two wires connected to it.  The large wire goes directly to the starter solenoid, and the smaller wire goes directly to the ammeter.  

Have you tried probing from the ammeter connection directly to the battery negative post; if ok, then to the ground stud in the trunk; if ok, then to one of the ground wires at the central ground connection under the dash?  


Last edited by jb1490

Steve. You were correct. It was in fact the the terminal in the front trunk. I can’t believe it but it was corroded. The car was not grounded.  

When I tested the terminal with the probe like John suggested it indicated no ground. The wire connected to the negative battery post however did indicate it was grounded.  

It looks like she is in fact alive. Many thanks!!

Also, when you have the time, it might make sense to check similar connections downstream from the positive battery terminal. That would be the solenoid on both sides, the starter, and the ground strap where it connects the chassis to the ZF.  All of those points are somewhat prone to corrosion. Cleaning those could prevent starting problems down the road.

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