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Discussion Starter · #1 ·
Hi All,

I got a 1972 chevelle and one day while driving the car completely shut off on me . I thought it may have been the battery but the battery was good then i decided to push the car back into the yard by putting the car in neutral, all of a sudden power came back on in the car and I was able to start it. A friend of mine told me it may be the neutral switch, however the neutral switch should not prevent the entire car from not getting current. I my case the neither the horn nor the dome light was coming on. There was not any power in the entire car. I'm really perplex by this.
The same problem cameup again when I tried to start the car in neutral this time it came back on when I played around with the steering column.

Please if anyone can help me troubleshoot I would greatly appreciate it.


:confused: :confused: :confused: :confused: :confused:
 

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You should have 2 main power wires from the battery. One that goes to the starter and one that goes to the horn relay. Chances of both going bad at the same time a fairly unlikely. It could be a couple of things. I would start with the battery, when you are experiencing the no start / no power situation check for 12 volts at the battery. Cells can go bad and make intermittent power. I had a side post battery where the lead insert had come loose and was causing this exact problem. Your starter solenoid might also be going bad. ** After reading your post again you said “ while driving the car completely shut off on me ” makes me think you may have some ignition switch problems. If the car was running the alternator would have kept it running even if the battery had an intermittent problem. This and a bad ground from the battery is about the only things I can think of that will shut the whole car down.
 

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Someone correct me if I'm wrong, but didn't they change the main junction location in '72?

I had a '77 Impala that did things like this to me. I found that I had a slightly loose nut on the main junction at the starter.

My point is that you should check all connections and cables between the battery and the main power sources. Don't neglect the negative (ground) side either. None of this is switched, it's directly connected, and should provide power at all times if the cables and connections are good.

If these all check out, take a look at your main fuse block. Maybe the power to the fuse block (where it goes through the firewall) has a bad connection. That will definitely shut everything else down. Might be as simple as loose bolts on the fuse-block.

If it were in the ignition switch, the lights, dome light, and the rest of the system wouldn't shut off along with the engine.
 

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Do you have the small ground wire from battery (-) to the inside right fender? If not you could be loosing the ground to the alternator bracket.

If you do have the small ground strap it sounds like the line from the starter to the horn relay may be the problem. Maybe the fuseible link connection is intermittent. (The 72 only has one lead from the battery).
*Edit*
Thinking about it the positive line from the starter shouldn't affect a running car. The alternator wire should keep it going. Check out the ground lines I mentioned first.
 

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I had a fusible link at or near (don't remember exactly) my horn relay. Lost AAAAAAAALL power... no lights, wouldn't crank...nuddin'. I was able to run a wire directly from my battery to my HEI and touch the battery and switch connectors at the solenoid to start it up and drive it home. Then it was just a matter of cutting out the link and replacing it with a piece of wire with a fuse holder.

Fusible links are a bit thicker/softer than standard wire. By gently bending it I was able to feel where the wire just burned away inside the insulation. Might be worth a look for you. Ultimately I just replaced my 30+ year old engine harness with a new one from M & H fabricators.

Good luck,

SKIP
 

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Discussion Starter · #6 ·
Thanks Everyone for the replies. I will do as you all suggested coming this weekend (yes I'm a weekend road warrior).

I will get back to you all on the results.

Thanks
newwit
 

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Discussion Starter · #7 ·
Thanks everyone for your replies.

It seems that the problem was a grounding issue or and electrical short. I did two things,
there was a wire connected to the horn relay which ran to the inside of the car, however it was not connected to anything. This same wire was touching the frame of the car so I simply disconnected the wire. Secondly i had an alarm installed a few months ago the power source was never connected (so I ruled this as not the problem). But just to make things sure I completly removed it.

After that I was go to go.....

Thank for all your help ..
 

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Discussion Starter · #8 ·
My nightmare has returned but this time it has gotten worst. My starter is now starting with some hesitation, before it can crank over. When I do get it to start, after driving it for a while, if I turn on the headlights or use the indicator I lose current in the car(totally), eventually causing the car to shut off. When this happens the current in the horn relay dies. After leaving the car to sit for some time current comes back on. Any suggestion ?

Also if I don't use my headlights or indicators I still lose power when time comes to restart the engine after driving for a while.

I think probably some wirer may be overheating that runs to the starter i will take a look over the weekend. Is there anything i may be missing?
 

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I had the same problem with my 72. Got out of school and it wouldnt start finally got it to start and it died just when i pulled it out of the parking lot.Your problem my be with a shorted out wire under the dash. It sometimes gets a little cramped under there around the steering column. Electrical problems my be the most frustrating thing to do on a car, so dont sweat it you will get through it I know how you feel. good luck.
 

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If you are losing power at the horn relay, the fusible link next to the starter may be broken.
 

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Hey Newwit,

Well, I was an ASE certified master tech for 10 years, until I quit to go to school (UC Berkeley) and get a masters in electrical engineering, so at the risk of coming off like a know it all, here are some things to consider.

A good analogy for the electrical system is a water source (the battery), a water pump, (also the battery. It not only provided the electrons to run the system, it provides the electrical force to move them)and a plumping system. The plumbing is the wires, and the on/off valves are the switches. Things like lights horns, starter motors, etc., can be thought of as controlled water leaks in that they lose power when operating. If a pipe breaks, then whatever faucet it goes to will not work. If a wire breaks, then whatever device it goes to will not work. This is called an OPEN circuit. If two pipes managed to fuse together so that they shared the water, then whatever those pipes were supposed to run would now act very different. If two wires fuse together so that they share current, this is called a SHORT circuit. With those ideas in mind, lets define a few terms so we can talk intelligently. It is frustrating to mean to hear people use volts, current, and power interchangably. They have distinct meanings, and they are not the same. If you can't decribe it accurately, you probably can't get any good information on how to fix it.


Voltage. Measured in Volts. This is the force that pushes the electrons around the electrical system. (yes, it really is a force)

Current. Measured in Amps. This is the flow of electrons. No electron flow, no current. Note that this does not mean you can't have voltage.

Resistance. Measure in Ohms. This impedes the flow off electrons. A high resistance requires more volatge to push the same amount of current.

These three are related by Ohms law,

Voltage = Volts x Resistance

Current by itself cannot do any work. It needs the voltage to push it. Voltage by itself can not do any work. There must be a current path (the wires, etc.) for the voltage to push current through before any work can be done. This brings us to the next thing, which is power.

Power. Measured in Watts. Power is Voltage times Current. If your starter draws 20 Amps, and your battery has 12 Volts, then the power required to turn your starter is 12 V x 20 A = 240 Watts. Similarly, A 3W tail light used on a 12 Volt car uses a current of 3W /12V = 1/4 amp.

OK. If your whole system goes dead, then it can only (yes ONLY) mean that the power source (the battery) is no longer connected to the car. Either the battery is dead (no Volts to push current) or the wire(s) feeding the car is (are) open. (no current can flow) No current or no volts means no work can be done. SO, look at the source and the wires from the source. Load test your battery. Nothing else will tell you for sure if it is any good. If it is good, examine the starter cable to the solenoid. Be very suspsicious of all connectors. The electrical definition of a connect is: "A highly unreliable device the joins two or more moderately unreliable devices". Look at them closely. With your kind of problem, 90% of the time a battery or battery cable is at fault. Make sure that the nuts bolting the wires to the solnoid are clean and tight. I once spent days talking a guy through a similar problem before he finally admitted he had spliced his ground cable. You can't do that and expect it to work. Keep in mind that enough power is flowing in the battery cables to start your big V8 beast. They and their conections must be in good condition.

The postive battery cable is for your starter. The smaller wire (on my 67 it goes to a junction block) runs everything else. As you can see, both wires have to fail for the whole car to go dead. (at least on my car they do. most cars are similar)

Get the wiring diagram for your car and learn to read it. It is not as easy as it sounds, but once you get the knack of it, you will be miles ahead of the folks who use guess work. Test the battery. If it is good, then start working down stream from there. Use a volt/amp meter to test things as you go.

Here is a good seat of the pants technique for finding a bad battery or battery connection.

Turn on the headlights.
Try to start the car.

If the headlights go dim, then the wiring to the starter and solnoid is good. They went dim because the starter is drawing a lot of current. leaving very little for the lights. Suspect a weak battery (but you already load tested it, right?)or a bad starter.

If the headlights go out, you have a bad connection somewhere between the battery and the starter, or a bad ground cable from the battery. You may have a bad battery, but you already load tested it, right?

If the headlights stay the same, then no current is getting to the starter. This could be the wiring, the ignition switch, or the starter itself.

As someone else has pointed out, fusible links that have burned out can be easly found by simply giving a good yank. A good one will hold, a bad one will pull apart right where the broken wire is located.

OK, this is a huge subject, and there is a huge amount misunderstanding, wrong ideas, and just fuzzy thinking out there when it comes to electrical systems.

I hope you find the problem, and I really hope that you know you found and fixed it. If you guess at it until it goes away, it will be back, as you have already found out.
 

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Discussion Starter · #14 ·
Thanks sidlev for explaining how the electrical system works. Sorry about using the wrong terminology.


All right lets get down to what happened this weekend. I did as John and everyone suggested by taking a look at the fusible link on the starter. The connection to the starter appeared to be fine, however on the other end of the 10 gauge wire there was another fusible link that ran to the horn relay, On further examination the connection between the wire and the fusible link was exposed and on the verge of breaking off. (probably causing a short somewhere). Consequently, I replaced the fusible link at the horn relay.

Question, is it correct for fusible links to be connected on both sides of the 10 gauge wire?


After starting the car the hesitation with the starter still persisted. My friend recommended that I start the car while he turned the distributor. After doing that we were able to get the engine to fire up on each try without any hesitation (one problem solved).

Now concerning the no voltage situation at the horn relay I’m assuming the bad fusible link may be my problem. I will have to wait and see. However, I did turn on the headlights while the car was running and it was fine. I recently got a new battery so I ruled that out as a problem. I will have to monitor the situation.

Question, out of curiosity where can I locate the voltage regulator in a 72 chevelle?

Thanks everyone for your input ….

I will keep you all posted …….
 
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