Last week I went into work and truck would not shut off. Take key out and it stays running. I had to put it into 3rd gear and let clutch out to kill engine. After that it would start and stop just fine. Next morning I go out and find a dead battery. So I figured ignition switch was acting up. Charged battery all seemed fine. I went to Oklahoma over weekend on vacation. Left truck in driveway. I forgot to disconnect battery. It didn't die. It has been starting and stopping fine since, but decided to put in a new ignition switch and lock cylinder since keys were worn anyway. Hooked everything up. Truck starts and stops fine like 5 times. Went to pick up dinner and truck wouldn't shut off. Any ideas as to what else besides the ignition switch will keep power going to the coil without key even in the truck? It is stock ignition: points, stock dist., stock type coil. Truck is 73 F100 with 302/3-speed. any help would greatly be appreciated.

 

Im not 100% on this but what about the voltage regulator?Maybe when you turn the key off the alternator is still feeding the coil power.



Tim

 

How would it do that ?

If the switch and tumbler isn't faulty you have some indepth trouble-shooting to do.

Power cross-over to ignition is usually hard to find.

First off.... eliminate the actual Ign switch from the equation by un-plugging it.

Then do a primary circuit of coil test.

No power to the coil..no engine run

 

There is two small wires going to the starter solinoid on right fender. The front wire is for the signal to it from the key switch, the one towards the rear (brown wire) gives ign module power while cranking/starting. Your starter solinoid is probably stuck some way that it is feeding power to the rear brown wire. If youn kill the engine by puting it in gear it still feed the ign module power untill it kills the battery. Next time it dose it pull the rear brown wire see if it dies. I have had it happen to me before.I replaced the starter solinoid

 

Was it actually running properly or dieseling? When the carb is not adjusted properly or the engine badly in need of a tune-up you can get what is called run-on or dieseling. Usually accompanied by a horrible smell.

 

It think it is fairly obvious that you have power to your coil even though your ingition switch is turned off. Otherwise, there is no possible way that it could run. Also, if I understand you correctly, it keeps running fine and is not running on as one would put it. You need to find out how the power is getting there. You can eliminate the alternator from the equation by unplugging all the wires to it. If your problem goes away it is probably the alternator. However, before you waste your time unplugging this, that, and doing all this stuff that probably won't work. I would buy a good book with a good wiring diagram and see which circuts shares your coil's power wire and start eliminating one thing at a time.

 

Without actually tracking down the problem myself, I'll be the second in the group to vote for the intermittently sticking solenoid switch. Cheap fix if it is the problem and if it turns out to be something different, it doesn't hurt to have a spare one in the glove box anyway.

 

I know with my mallory ignition the voltage regulator/charge light can keep the ignition powered up, Can it do this with the stock ignition??? Mallorys fix was a diode on the regulator wiring

 

Please explain to me how the alternator affects the ignition ?

The ignition system normally gets it power from the "battery" through key > resistor type ignition wire .....not from the alternator.

NOTE: You can blow diodes in the alternator if the harness (from to to the battery) isn't hooked up to the battery..... with the alternator turning.


The checking of the I terminal connector is a good thing to do.

Because His problem is: "Power to the coil" with the Ignition key OFF.

This means the Ignition switch is faulty (MY Though even though he replaced it)
or
There is another source of power to the coil from the ignition switch....other than the normal position on the Ignition switch.

As stated in my other reply.

The charging system has absolutely nothing to do with ignition.......
2 different systems.

The fact that the battery went dead once the wire he said was removed......proves this.

 

Thanks for all the replies so far. Truck hasn't acted up again yet to test all these things which is really annoying to me. I might go ahead and replace starter solenoid. As far as the whole alternator idea I agree with what Mil1ion says. The only time I've seen power to coil after ignition shut off from alternator is with MSd igniton or mallory as someone stated and solution is diode in alternator wire, but this was only in cars/trucks with starter solenoid on starter not seperate as in the ford trucks. Alternator causing this would be a shock at best at this point. I will probably replace solenoid just because it is cheap enough to do so. I really am hoping it acts up again so i can eliminate ignition switch from the problem though.

BTW: I don't have engine "run-on" as Torque1st suggested. When I have the problem the engine is running normally as in I can take key out and still drive around the block.

Thank you for all the suggestions. I appreciate it.

 

Mil1ion,

It depends on how the system is configured. On a lot of appilcations the switch at the key normally turns on the field to alternator and the positive side of the coil at the same time. If for some reason the alternator (normally only internally regulated alternators do this) has an internal transistor problem it will allow the alternator field wire to stay powered and that will provide 12 volt to positive side of the coil which will keep the truck running. Once again depending on the wiring configuration, it will keep the electric fuel pump going too. Also, once you finally do get it turned off, the alternator field will stay hot no matter if the truck is on or off because of this problem and eventually drain the battery. It can happen and does occur. While I have never seen an externally regulated system do this, I have seen several of the internally regulated systems do this when they have a regulator problem on several different manufacture's of cars and trucks. It all is dependant if the field wire to the alternator is shared in the same ciruit as the coil. If they are not on the same circuit, it is impossible for this to occur as you said. If they are, then it is very possible that this can occur. As far as alternators diodes failing from this test is possible, but not very likely to happen due to the short duration of the test at hand. And, if it is internally regulated and the truck turns off, you just found your problem and need a new alternator anyway. But how many times have you replaced an externally regulated alternator's regulator and not had to replace the alternator? I have a bunch of times and when a regulator is bad often times it is the same thing as unplugging the alternator from the system and no damage was done to the alternator.

 

Finally the truck acted up again today. Pulled ignition switch connector. Stayed running. It shut off as soon as I pulled wire off "I" terminal of starter solenoid. I replaced soleniod. Hopefully that will solve all my problems for awhile. Thanks for everyone's help in my last post. It was greatly appreciated.

 

quote:

It depends on how the system is configured. On a lot of appilcations the switch at the key normally turns on the field to alternator and the positive side of the coil at the same time. If for some reason the alternator (normally only internally regulated alternators do this) has an internal transistor problem it will allow the alternator field wire to stay powered and that will provide 12 volt to positive side of the coil which will keep the truck running.

~~~~~~~~~~~~~~~~~~~~~

But how does this dso it.
What configuration ?

Here is the Ignition system ..please show me how except for from a Faulty Ignition switch
how power would get to the coil .

 

Well, it can't on your simplified wiring diagram. If you actually trace your ignition wire on a real truck you will find that it has taps from the factory. Also, you could take a look at a better wiring diagram that actually shows everything and I think that you would see that it is possible. The black yellow wire from your switch is spliced into the red green wire And also your brown wire form your starter relay that goes to your alternator regulator and to your alternator light. It also is spliced in to your positive side of you coil. Unfortunatley your diagram doesn't show that, but it does do this on many 70 ford trucks. If for some reason the regulator fails in a particular way will you have power going to you alternator at all times If it does this just the right way, you are going to find it very difficult to turn off since you now essentially don't have a switch in the system anymore because your alternator is powering everything. It is also likely at this point that you have a run away chargin system -meaning it is charging much more than 13 or so volts. Also, do remember, a 1974 truck is getting pretty old and you never know what has been changed. I have seen (as I bet you have too) internally alternators wired incorrectly into externally regulated systems. I have seen alternators with external regulators still hooked up to internally regulated alternators (sometimes they even work somehow). I have seen one wire summit alternators installed on the positive coil wire that have failed. This is not to mention the countless wire taps that well meaning folks put somewhere in between. People that work on their own cars often change how things are set up. And this is OK because it is their car. However, it makes diagnosis a little sketchy and not as clean, cut and dry as you would like...for that matter as I would like either.

 

Quote: And also your brown wire form your starter relay that goes to your alternator regulator and to your alternator light. It also is spliced in to your positive side of you coil.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

No it isn't, it gets 12 volts thru the key in start position only, after that it is resisted to 8.5 volts thru the pink resistence wire coming from the ignition switch.

This is the actual FORD wiring on the truck in question.

The way Ford puts it in trucks.


The main harness wiring from the relay goes to the fuse box to power the whole truck.

Battery power from the VR & Ammeter or Idiot light....goes thru red/yellow wire .... to the Ign. switch.

The ignition system gets it power from a special ignition key position in start and in run position.

The battery ran dead because there was power being fed to the ignition system with the Key OFF.

Yes, The alternator (Not spinning) even with a bad diode *shorting out* can cause Battery drrain.

But, so can a bad ignition switch sending power to the coil with the key in the off position .......as well as a Bad Starter relay which allows power to feed thru to the coil.

But that isn't an Alternator source.

Everything to the ignition goes "Thru the switch or
Starter relay (in start position only) " no where else.

Coils burn up from constant 14.5 volts

I'm not convinced the charging system is part of the ignition system.

I have always believed they are seperate as per all the diagrams I have ever looked at .