1972 car starts and dies - towed home

[Edward J.]

Re: 1972 car starts and dies - towed home

Larry, I will give you quick test of the wiring. The coil should have power with the ignition switch in run position this is the wire coming from switch and heading out into engine compartment, so if there is power at the + side of coil, that side of wiring is okay, the next is the start position of ignition switch the solenoid engages and feeds the coil the full 12 volts. This wire comes from the solenoid R terminal and heads up to coil and is tied in with the resistor wire on top of coil from fire wall. good luck

[Larry M.]

Re: 1972 car starts and dies - towed home

Ed,

Thanks; yes, that's my difficulty. The engine would crank and run with the key in the 'Start' position. When the key is released and goes into the 'Run' position, I lose power to the coil and the engine dies.

I've been trying to confirm what portions of the circuit are good or bad, and have worked my way back to the ignition switch. I can't identify which wire supplies the switch with power. The circuit from the switch to the coil seems good.

Larry

[Edward J.]

Re: 1972 car starts and dies - towed home

Larry I have not looked back to all the posts here. but I think you said a few posts back with the key in the on position you had power to + side of coil???

[Larry M.]

Re: 1972 car starts and dies - towed home

Ed,

I have power to the positive side only when the key is in the 'Start' position (post #8).

Since my earlier post today, I've been looking again at the wiring diagram, and it looks like the brown wire with white stripe is the one that provides power to the ignition switch.

I just checked that wire for continuity from the firewall to the switch, and it checks OK.

I now need to see where on the engine side of that wire I lose power (if in fact the brown/white is the power supply wire).

Thanks again for your help.

Larry

[Edward J.]

Re: 1972 car starts and dies - towed home

Larry, Take a look at the harness at coil + side in engine compartment should be black and pink. (is the resister wire). And I believe it brown and white on the other side of firewall to ignition switch. Check to make sure I have the colors correct. This the wire that when key is released from start feeds the + side of coil. Larry was looking at the pic of the ignition switch harness you do have a brown and white wire, does that terminal have some corrosion? It may just be the pic.

[Larry M.]

Re: 1972 car starts and dies - towed home

Ed,

Thanks again. I've checked the continuity of the brown/white wire from that connector to it's terminal on the engine-compartment end of the wiring harness, and it checks out OK.

I don't think corrosion is an issue; I probed the wires at the white connector at the switch from both sides with a test light and didn't complete any circuits.

I'm going to clean up for the day and watch the football playoffs. I'll return to this project later on this week.

I appreciate your assistance.

Larry

[Edward J.]

Re: 1972 car starts and dies - towed home

When you test the brown and white wire at the ignition switch connector they must be plugged into switch and the switch turned on.

[Larry M.]

Re: 1972 car starts and dies - towed home

While I'm taking a break from the actual work on the car itself, here's the logic of my troubleshooting -

A circuit needs to be completed to power to the + side of the coil with the key in the 'Run' position.

Whatever that circuit is, it has what I'll call four components - two on either side of the firewall. There should be:
1. Power from the engine compartment (starter solenoid) to the bulkhead connector.
2. Power from the bulkhead connector into the ignition switch.
3. Power from the switch, when engaged in the 'Run' position, out to the bulkhead connector.
4. Power from the bulkhead connector out to the + side of the coil.

Does that sound correct, if in a simplified manner?

I have confirmed continuity in the wiring that makes up my sequence #'s 3 and 4. Electricity can flow from the brown/white wire at the switch, to the terminal at the coil.

Where I'm stuck now is identifying which wires bring power through the bulkhead and to the switch (#'s 1 and 2).

Any ideas?

Larry

[Edward J.]

Re: 1972 car starts and dies - towed home

Larry, I believe it is easier to start at the br/white wire at switch. 1. The br. /white wire is powered with the key in on position ,2.From switch this wire heads through the fire wall and out to coil, which is where there should be 8/9 volts( if you have a volt meter) at coil . as I see it these are the only steps you need to locate the open in circuit.When I say the key is turned into on position this should be the first click of the switch , Not the starting position because this is the by-pass circuit when starting, which you will see full battery voltage during cranking.

[Larry M.]

Re: 1972 car starts and dies - towed home

Ed,

Thanks, I'll try that tomorrow after work. But, hasn't what I've tried already confirmed that there's no power at the switch?

Since I have no power at the coil, and the wiring from the switch to the coil will carry current, doesn't that indicate no power at the switch? And if so, I'm back to my other question of what wire provides power to the switch, so I can backtrack from there.

Larry

[Edward J.]

Re: 1972 car starts and dies - towed home

Larry, the brown and white wire only carries current when the ignition switch is turned to on position, I do not have a dia. in front of me but there will be a wire that carries battery voltage on the switch connector so when the switch is turn that wire will become a live wire..

[Larry M.]

Re: 1972 car starts and dies - towed home

Ed,

Thanks again. I will do that when I get back to the car. Might not be tonight.

Larry

[Paul O.]

Re: 1972 car starts and dies - towed home

Larry

Everyone that has posted has given you great information. I have had this following problem occur a few times during my electrical trouble shooting days. Not saying this is your problem but it is one that we all should be aware of.

1. The wiring in a Corvette or most any vehicle is stranded copper wire not solid wire.
2. If by chance at any point if all but one strand in the wire is left making a connection the following would/could occur.
3. Ohm meter check could show a normal reading in continuity. Voltage could indicate normal very low to no voltage. But current to do the work does not have a large enough area to flow enough electrons.
4. This could also happen at any connection point such as a switch, bulk head connector etc.

Continuity does not always indicate a that a wire, connection or circuit is in good condition only amperage and voltage will give you an accurate indication the work the circuit can do.

[Larry M.]

Re: 1972 car starts and dies - towed home

Paul,

Thanks; I appreciate your points.

I don't think I'll be working on the problem again until this weekend. A few days away from it may refresh my attitude and motivation.

Right now it's a frustrating issue to work through, in no small part because of my ignorance in diagnosing and repairing electrical problems such as this. A broken or damaged item that I'm able to see and touch is a much easier fix!

Larry