Hey all, im a bit new to the board posting but i have lurked for a little bit.
I have a 91' 7.3with a couple of irritating problems. My biggest concern is a short that will drain the batteries dead in day or so of sitting.

I was installing the door panels and some all new switches to get my windows working when i noticed the windows will work with the key out of the ignition. WTF thats not normal.. Also sometimes ill turn the key a few times and nothing at all will happen then on the third time she wakes up. Also have to turn it pretty far. So since its pretty common for these ignitions to go bad i thought i would replace it.

Could the ignition (key) be my short?

Ignition switch: Ford basic part number: 11572

Ignition cylinder w/keys: Ford basic part number: 11582
(thanks numberdummy)

What ya think?

 

Sometimes they short out and just plain wear out over time to the point where u dont even need a key to start! or if have to key start and u can pull it out...

did u try testing with a test light or a DVOM?

 

You may have a switch problem, or it could be the rod that runs from the key down to the switch.

The actual ignition switch is under the dash on top of the steering column.

 

Thanks for the ideas. I haven't been able to mess with it lately because my MarkVIII hvac was smoking a bit. The electrical flu seems to be spreading.

A DVOM is probably the right way to test for it but honestly i don't have much experience with those things. Hook it up and start pulling fuses until it stops pulling juice with the truck off? Hook it up between the battery ground?

What should i look for when buying a meter?


Im going to replace the switch anyway, that thing is too buggy to just live with.

 

You can get a digital voltmeter at a lot of different places. Home improvement centers, Radio Shack, etc. for around $20. Look for one that will handle 10 amps. (hopefully your short circuit won't be pulling more than that). Most meters have one positive lead connector for reading volts, ohms and low-current amp readings, and a separate connector for 10A measurements. Make sure your positive meter lead is connected to this plug.

Disconnect both batteries then connect the positive lead of the voltmeter to the battery's positive terminal then the negative lead of the voltmeter to the battery cable. See what kind of current your system is pulling (normal would be around .25 amps or less).

Don't turn your key on or the current the glow plugs draw will smoke your meter and its leads. You should also tape or otherwise fasten your door jamb switch down to prevent the dome light from coming on.

Start pulling fuses until you see your current reading drop to normal. If I get a chance, I'll take a reading on my system to see what it pulls when everything's off. Things like your stereo memory, possibly the transmission computer, the door chime, and other devices like that will pull a small amount of current all the time. If you're reading several amps and it suddenly drops to something like a half amp or quarter amp when you pull a certain fuse, then you found your problem circuit.

 

Another idea is to put a test light in the circuit. I put in the ground circuit. Like Matt said pulls fuses.

When it comes to meters that depends on what you are doing. The old analog meters worked great but don't use one of them to check a solid state circuit. They can fry one. Solid state is circuit card things. Digital meters are pretty much the best way to go but watch using them to test diodes. Make you are in the right function for that. The impedance is high enough of most that will tell you a diode is bad when it isn't.

 

Auto ranging on the volts scale is nice.
Also fuse protection for the leads is very nice.

Fuses are much cheaper than meters.
To much juice blows the fuse.

For my automotive use, I have a Digital Micronolta from Radio Shack that I paid about 60 dollars for 15 or so years ago.
I like it for testing glow plugs, the ohms read down in the .01 range.

Almost as nice as my much more expensive Fluke I use for AC circuits.

 

Ok guys ive been gone for a bit but i have tackled this on and off.

I replaced the the ignition switch and key. It was definitely time for that anyway but it didn't solve my electrical short.

While just going through the engine bay i noticed some wires going to the AC compressor that had been previously tapped by the PO. They had been worn through because both cables had been rubbing against the AC bracket and getting squeezed by the hood. I can see where the insulation on the hood was getting a hole. So i tapped those up nice separate with like a roll of electrical tape (lol nah not that bad) and then i zipped tied the wires out of the way. Problem is i had no reading before i did this. I don't know if this solved anything.

I followed Matts directions and no matter what fuse i pull i still get 1.44 . Thats way above normal I'm thinking. I only checked with one battery (drivers side) while the other was completely disconnected. Is this correct? I bought a meter from an auto parts store and its not bad but its no Fluke thats for sure. I set it to amps and started pulling. Honestly i hope its some simple im doing wrong to get that 1.44

I guess i could just plug it up again today and tomorrow be depressed when it dosent crank again...eeeerrrrrrrr.

 

Try disconnecting the alternator and see if any difference.

 

I had cranked the truck up and took it for a mind clearing ride and while i was out i thought hmmm alternator. Then i get back and read Lazy k's post; weird.

Well i disconnected the clip two wires to the alternator and she pulls nothing. Finally we are getting somewhere. Thank you sir..

So my next question is ; now what? look for a short running to the alternator?
Is the alternator itself my culprit? Is something not grounded?
Electronic control unit? It look s buggy, theres a wire that seems to have a slight air gap in the connection there. Ill fix that now.

Beat it with a hammer?

The last one really only works on suspension but it can do wonders for stress.

 

I would say that the alternater is toast. Take it an auto parts store to have it tested .

 

Well the alternator is maybe a year or two old. I changed it myself with a new motorcraft. Also i noticed when i stick a test light into the two wire connector that plugs into the alternator there is constant juice. Is that normal? What controls the electrical flow ?

 

With the key off both wires should be dead. Key on engine not running the orange with blue stripe should be live. Does the alternator feel warm before you run it? If so a diode in the altenator could be burned up. If so the alt. would still charge but woul drain the battery when not running.

 

Ok i found and solved the problem. I replaced the ignition control unit (black device on firewall with wires bolted to it) and the voltage regulator (ah ha....yeah silver box with a wire clip stuck in the side also by the ignition control unit)

I dont regret replacing what i have since she has 200+ miles and all those things are ratty.

Ultimately my short or voltage draw was caused by the voltage regulator 16.00 and its done.

Thanks to all for the help and especially for schooling me on voltage meters and troubleshooting.
Sick as it sounds i started to enjoy it....