The Ford Barn

The Ford Barn (https://www.fordbarn.com/forum/index.php)
-   Model A (1928-31) (https://www.fordbarn.com/forum/forumdisplay.php?f=3)
-   -   Dead Short - how do I find it? (https://www.fordbarn.com/forum/showthread.php?t=260513)

31 Woody 03-16-2019 11:16 PM

Dead Short - how do I find it?
 

Looks like the Woody has a dead short. I do have a cutoff switch, but I must have something amiss with that too or something. With the master cutoff in the off position and the ignition off, the leads to the coil spark when touched to the coil positive and negative. I found the issue today after a short drive, then parking in the driveway while I lubed the chassis. The car wouldn’t start. After some troubleshooting I found the coil to be extremely hot to the touch. I disconnected it (the master switch was ON all this time). I noticed sparking when I connected the new coil. The car started up and I was able to back into the garage which is uphill.

Once in the garage I turned off the ignition and the car shut off as normal. Then I killed the master switch and turned off the fuel. A short time later, the replacement coil was hot too! I disconnected the leads and they sparked! So, the battery is now disconnected.

Where do I start? All I can think to do is disconnect about everything—which isn’t much and then start closest to the battery reconnecting stuff until i get a spark, then check that wire for a bare spot or ground fault. Any better ideas?

Jim/TX/GA 03-16-2019 11:28 PM

Re: Dead Short - how do I find it?
 

Is the master cutoff switch installed in the ground cable or the cable between the battery and the starter switch?

Is your ignition switch an original style pop-out switch or an aftermarket key switch?

31 Woody 03-16-2019 11:49 PM

Re: Dead Short - how do I find it?
 

The cutoff is between the battery and starter. The ignition is a pop out, but as I stated, the car shuts off when the popout is pushed in and it won’t start in the off position either.

I am thinking a ground kill may be a better arrangement on the cutoff.

Mike V. Florida 03-16-2019 11:55 PM

Re: Dead Short - how do I find it?
 

From just reading your problem it appears you have two problems.


1) your master switch is not working. If it was, you would have nothing getting to the wiring.


Take a meter of a test light and place it across the leads of the switch. Switch on, no voltage/light. Switch off, voltage/light on.


2) your ignition switch is shorted. The coil gets power from the switch. If the switch is open then nothing can get to the coil and down to the distributor. Take a piece of paper and put it between the points. Take your meter/light and place it across the points. With ign switch off you should have no voltage/light. Turn on the ign and make the reading you should have voltage/light.


Please report back. Oh break out the wiring diagram, here is one, http://www.fordgarage.com/pages/awiringdiagram.htm

The Master Cylinder 03-16-2019 11:59 PM

Re: Dead Short - how do I find it?
 

That is an odd one. Since you are still getting power when the Master S/O switch is off, I would start by checking it. I think you may have another problem also but check the Master S/O switch first.

The Master Cylinder 03-17-2019 12:00 AM

Re: Dead Short - how do I find it?
 

Mike is faster... :p

Jacksonlll 03-17-2019 05:52 AM

Re: Dead Short - how do I find it?
 

Sounds like you have two problems. Make sure the batt cable is not touching anything on the way to your master switch. Probably a master switch that is not breaking the circuit. With the key off, there should not be power across the coil. Chase that one. Both posts should be hot, but the coil is not drawing any current. It can't get hot.

Jim/TX/GA 03-17-2019 06:50 AM

Re: Dead Short - how do I find it?
 

Quote:

Originally Posted by Jacksonlll (Post 1737126)

<snip>

With the key off, there should not be power across the coil. Chase that one. Both posts should be hot, but the coil is not drawing any current. It can't get hot.

Maybe, maybe not! It depends on how you wired the car. Ford's original wiring scheme has battery power supplied to the coil all the time, and the key switch interrupts the wire between coil and points. So if wired it per the original schematic, you turn the switch off and the coil still has voltage on it! (but you are correct, it should not get hot)

"Modern" car ignition wiring schemes usually put the key between the battery and the coil. But not Henry! :confused:

.

Jim/TX/GA 03-17-2019 07:09 AM

Re: Dead Short - how do I find it?
 

Quote:

Originally Posted by 31 Woody (Post 1737106)
The cutoff is between the battery and starter. The ignition is a pop out, but as I stated, the car shuts off when the popout is pushed in and it won’t start in the off position either.

I am thinking a ground kill may be a better arrangement on the cutoff.

If the engine stops when you push in the pop-out switch, it is successfully breaking the connection between the coil and the points... but if the switch is defective (or if the wires inside the instrument panel are shorting out) the coil is still finding a ground in there somewhere.

So I suspect the problem lies inside the instrument panel, ether switch or wiring.

I also suspect your master switch is defective. Test with a meter. It may not allow enough current through to crank the starter over, but it is allowing 5 amps through the coil.

Hope that helps.
.

Jim/TX/GA 03-17-2019 07:19 AM

Re: Dead Short - how do I find it?
 

Quote:

Originally Posted by Mike V. Florida (Post 1737108)

<snip>

2) your ignition switch is shorted. The coil gets power from the switch. If the switch is open then nothing can get to the coil and down to the distributor.

<snip>

Please report back. Oh break out the wiring diagram, here is one, http://www.fordgarage.com/pages/awiringdiagram.htm

Ummm, no, the coil does not get power from the switch. Go study that wiring diagram again. The coil gets POWER from the terminal box, all the time, via the black wire. The switch provides a GROUND to the coil, with the red wire and through the points, when it's turned on and working properly.

So if the switch is defective and providing a ground, or if the red wire from coil to switch is shorted to ground, the coil has current running through it and will get hot. :eek:

.

31 Woody 03-17-2019 01:52 PM

Re: Dead Short - how do I find it?
 

UPDATE: I didn’t think it was possible, but the master cutoff switch is allowing a tiny bit of voltage through. 0.01-0.03 volts. I have the same type cutoff that they put on the back of race cars, guess I need something better. Now on to the second problem—guess I have to pull the dash apart and check wires for bare spots or something. I do have a second pop-out switch—I figured since the car won’t start when off and it turns the car off when I push it in it was good. Thoughts?

Jim/TX/GA 03-17-2019 07:04 PM

Re: Dead Short - how do I find it?
 

Quote:

Originally Posted by 31 Woody (Post 1737279)
UPDATE: I didn’t think it was possible, but the master cutoff switch is allowing a tiny bit of voltage through. 0.01-0.03 volts. I have the same type cutoff that they put on the back of race cars, guess I need something better. Now on to the second problem—guess I have to pull the dash apart and check wires for bare spots or something. I do have a second pop-out switch—I figured since the car won’t start when off and it turns the car off when I push it in it was good. Thoughts?

Looking for (or reading with a meter) a short of the red wire to ground is a good idea.

The only way to know for sure if the switch is good or bad is to test it with an ohmmeter out of the car.

The original switches are supposed to break the connection to the points and ground the points only (not the red feed wire) when you push the switch button in. But with time, age, and use, things can get messed up inside and you can end up with the connection to the points opening up correctly (engine stops) but the red feed wire grounding out (which is not right, and is consistent with your symptoms).

HTH.

31 Woody 03-17-2019 07:52 PM

Re: Dead Short - how do I find it?
 

Testing revealed there was some internal grounding on the popout switch to the red wire. I installed my spare popout, tested it all again, put it back together, tested again to be sure, and fixed. So, both the master cutoff and the popout were defective. I think I narrowly averted a disaster!

And thanks to all for the help and suggestions—much appreciated. The color wiring diagram is going to get printed and laminated—it proved very useful today.

Jynx 03-17-2019 09:04 PM

Re: Dead Short - how do I find it?
 

Perhaps the wire in the distributor os grounding just like points burnt together


All times are GMT -5. The time now is 07:54 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.