Electrical fire, now to figure out why.

[Smokedtires]

Hello all, I'm kinda stumped and looking for ideas. My wire harness from generator to junction box burned up, then looks like it traveled to the ammeter.

I've replaced the generator to junction and the junction box to ammeter harnesses. I've now also added a 30amp battery fuse at the starter. I also added fuses to the generator cutout on both the junction side and the lights/horn side.

I am 6v positive ground. When I turn on the battery disconnect, the 30a fuse between the cutout and junction box immediately blows. The 10a on the light side has not blown yet. What could be causing this high current? I measured my ammeter which has 0.1 ohms resistance. I have a new cutout and ammeter ordered, but not convinced they are causing the high current.

The key switch measures 4.22 amps and 6.25 volts. 6.1v at ammeter with fuse removed to generator cutout. Over 10amps at ammeter.

[Smokedtires]

I also added a 10a fuse to the dash light which is currently working properly.

[29spcoupe]

Sounds like a dead short somewhere. Suspect mice chewing wires.

[Rob Doe]

If you'e had the wires off at the generator cutout, did you by chance get the fiber insulator left out or could the wires be hooked on the wrong side of the fiber insulator? I did that once.

The ig switch can touch the fuel tank and short. Cover the tank behind it. You can jumper between the two junction box studs to bypass the ammeter circuit if the box to ammeter and return connections are undone, etc. I see that you have the 30A fuse down by the generator rather than just after the starter switch.

I suggest unhooking wires to isolate sections of the circuit. Start with the horn and light switch wires at the generator. The pink/red wire from the + coil post to the ig switch can be undone at the coil to isolate the ig switch and the primary ig circuit all the way to the points. The yellow wire that goes to the ammeter from the junction box and the yellow black stripe from the ammeter to the box can be undone to isolate the ammeter circuit etc. You get the idea.

Others may make wiser suggestions.

[Smokedtires]

Thank you Rob Doe, I will try these. The ammeter had regular nuts, but now have proper ammeter nuts installed.

[Marshall V. Daut]

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Start simple: disconnect the wire from the headlights and horn at the generator cutout. Reconnect the wire from the cutout to the terminal box. Turn on the power. If the fuse blows again, the problem lies between the generator and the instrument panel. If it doesn't blow out, then the most likely culprit is a headlight connection. Also, wires may be chafing inside the metal conduits leading to the headlights and the horn. Check out all that wiring post-cutout forward until you have found a bare wire touching metal. If the short is inside the conduits, they will be hot to the touch if you temporarily hook things up without a fuse in-line. Keep the negative battery cable loose so that you can quickly pull it off the battery if a conduit gets hot or the wires start to get warm and smell.
If the headlight/horn harness and connections are not at fault after this test, disconnect the remaining wire from the cutout. Turn on the power with a fresh fuse. If the fuse still blows, you can rule out the generator and its cutout. The problem lies between the starter and the instrument panel. Take off the terminal box cover and look for wires touching metal, such as touching the metal ignition conduit, which should be enclosed against shorting against wires by a long rubber grommet. If the wires and connections look good and are tight inside the terminal box, pull the instrument panel forward. Check the wires to the ammeter and ignition switch. Tight? Can the ammeter posts be wiggled? If so, try tightening the bottom nuts and test again with a fuse. If the fuse still blows, you can eliminate the ammeter from suspicion by disconnecting the two wires on the back and putting them together by an alligator clip or tape. Do this with the battery disconnected. After tying the wires together in this fashion, hook up the battery again and check whether the fuse blows out. If it doesn't, then the problem is in the dash wiring or in the ammeter itself.
Also ensure that the negative "hot" battery cable end is not touching the metal battery holddown frame or anything else. Oftentimes that cable gets chafed by the brake pedal if the cable's bellhousing routing bracket with rubber grommet is missing or the cable is too long and rubs against the brake pedal.
By following what I have written, you are eliminating/isolating individual traditional areas of shorts and electrical problems. If none of these suggestions solves the problem, start checking wires and connections from the light switch bail to the stoplight switch and taillight(s). It is less likely that the short will be found here than from the headlights to the ammeter. Somewhere in your electrical system there is a short caused by a frayed wire or a "hot" wire connector coming into contact with something metal. It's there. You'll find it!
Marshall

[rotorwrench]

Something doesn't look right there. I'm used to seeing the output side of the generator bare of wires. The cut out is the only thing that connects to the the output terminal stud on the generator at the back there. The Gen wire, horn wire, and light power wire all generally connect at the front side of the cut out switch.

[Smokedtires]

Thank you so much. Will be following these tips as well.

[CWPASADENA]

A 10 amp fuse to the lights is not enough. This circuit also carries the horn, I would install a 30 amp fuse.

However, this is not what is causing the short.

My opinion,

Chris W.

[rotorwrench]

If a fuse is used on the battery side of the buss at the starter. No other fuse is really necessary. Fuse size is determined to protect the conductor wire and not the load. A 14 gauge wire should have no larger rating than 15-amps or the wire will not be protected against overload. This is from the AC43.13-1B chapter 11 page 11-15. Here is a Link:
https://www.faa.gov/documentLibrary/...-1B_w-chg1.pdf

[Tom Endy]

Here is how I go about isolating an electrical fault on a Model A.

http://www.santaanitaas.org/wp-conte...Quick-easy.pdf

Tom Endy

[Bob C]

Originally Posted by rotorwrench

Something doesn't look right there. I'm used to seeing the output side of the generator bare of wires. The cut out is the only thing that connects to the the output terminal stud on the generator at the back there. The Gen wire, horn wire, and light power wire all generally connect at the front side of the cut out switch.

He has the earlier generator with the output terminal at the pulley end.

[Dave in Petaluma]

Early car-i.e. 1928-'29-check your brake light switch. If your brakes are low the repo switch will short when the pedal is depressed.

[rotorwrench]

Originally Posted by Bob C

He has the earlier generator with the output terminal at the pulley end.

I'm used to seeing those on the ones with the ball bearing on the back. There must be some mixing & matching compatibility there.

[cavalierhome]

Originally Posted by Smokedtires

Hello all, I'm kinda stumped and looking for ideas. My wire harness from generator to junction box burned up, then looks like it traveled to the ammeter.

I've replaced the generator to junction and the junction box to ammeter harnesses. I've now also added a 30amp battery fuse at the starter. I also added fuses to the generator cutout on both the junction side and the lights/horn side.

I am 6v positive ground. When I turn on the battery disconnect, the 30a fuse between the cutout and junction box immediately blows. The 10a on the light side has not blown yet. What could be causing this high current? I measured my ammeter which has 0.1 ohms resistance. I have a new cutout and ammeter ordered, but not convinced they are causing the high current.

The key switch measures 4.22 amps and 6.25 volts. 6.1v at ammeter with fuse removed to generator cutout. Over 10amps at ammeter.

If you have a kill switch look to see if it is making contact with the frame under the car.

[ndnchf]

FWIW - that is an early cutout used October 1927 - January 1929. The photo is not clear enough for me to see if it is mounted backwards or not. But the open end of the feet should face towards the generator's terminal post or pulley end.

[Stretch Cab]

For what its worth, I can feel your pain. First car show after a 9 month total restoration, we took my early 30 Rdst. PU to an AACA car show. The night before the judging the wiring caught fire. Fortunately there was a flea mrk. so parts were available and plenty of help. Got it all back together and cleaned up and did well in the judging. That was 50 years ago and still have the truck.

[nkaminar]

Another thing to check is the armored cable where it goes into the junction box. It can short out the terminals on the junction box. There is supposed to be a rubber grommet there to prevent the short.

[rotorwrench]

The early cut outs were used on the powerhouse generators. The Autolite generator types came later. All this type of stuff is still out there though in various states of condition and quantity.

Nkaminar has a point about the metal conduit. It can be a source of grounding if not properly installed or if the wiring is getting questionable in condition. I think this may have been why Ford changed over to the flexible loom in 1930 or so. It doesn't take much to get an old frayed wire to short out. A lot of the new harnesses have protective shrink wrap insulation in key locations around the flag terminals and such. Ford wasn't always so good about wire harness protection. They should have used fuses as well. A lot of early cars burned up due to wiring problems and wood with lacquer paint contruction.

That conduit doesn't have a loose fit in the terminal box. I don't thing any form of grommet could be used there. The tube is flared where it enters the terminal box and it relies on the firewall and engine water inlet clamps to hold it in place. A person could put some electrical tape on there but that's about it the way they are currently made. I liked the old original cloth reinforced phenolic plastic terminal boxes better but no one makes them like that anymore.

[Smokedtires]

Thank you everyone. After checking everything, it looks like the cutout is causing the problem. I have a new one being delivered tomorrow so I will know more. Interesting all of the discussion on the cutout, that is how it was setup when I bought the car in June.

Your tips were all very helpful. Thanks again.

[ndnchf]

Originally Posted by Smokedtires

Thank you ever44-77yone. After checking everything, it looks like the cutout is causing the problem. I have a new one being delivered tomorrow so I will know more. Interesting all of the discussion on the cutout, that is how it was setup when I bought the car in June.

Your tips were all very helpful. Thanks again.

If its any help, I sell refurbished, original Ford cutouts. I can also test, and possibly repair yours. PM me if interested.

Steve

[nkaminar]

The grommet is here: https://www.snydersantiqueauto.com/p...6244&cat=41801

[rotorwrench]

That's for the armored cable. I was referring to the metal conduit that houses the generator wire and the battery wire on the 1928 and 29 models. The armored cable for the ignition uses the large grommet to stabilize the big wire wound flexible conduit. It also acts to limit moisture intrusion into the terminal box. It insulates only a small portion of the dash harneses against shorting in the area of the two terminal studs.

[Rob Doe]

This is a great thread for me. Thanks to all who have posted here. Rob