Brand new to the board and fairly new to model a’s

[Hipopinto]

Hey all

I have owned my model a coupe since 1999

It was a wedding gift from my late uncle (his first car)

It hadn’t ran for years when I got it he and I got it running fairly easily and basically for the past 23 years I would randomly drive it!

It’s never given me a lick of troubles until today!

It started blowing the 30 amp fuse I installed by the starter but not always instantly

This car is converted to 12 volts with and alternator

To get it “home” I disconnected the yellow wire at the alternator connection and the fuse stopped blowing. The car drove great and ran but I noticed there is no horn with this wire removed.

Electrical is not my best area but the electrical dosent get much more simple than this!

Is there a schematic available?

Any pointers where to look?

Thanks again all I look forward to replies!

Dave

[Clem Clement]

Welcome to the Barn! Does it have original wiring? Check for loose/shorted wires.

[Hipopinto]

Yes all wiring is original I realize it’s 91 years old but it’s in amazing condition for it’s age!

[Chuck Dempsey]

Yes, welcome to the 'Barn. A world of info here, I'm sure someone can help you out....

[Ernie Vitucci]

Good Evening...You most likely have a short someplace. Since it is running with the horn circuit removed, I would check all the wiring for loose connections, and or bare wire, where the insulation has worn off... in the horn area and the head light circuits...and look carefully at the fuse holder that you have on the starter. Some of those were purely made and become loose over time and need to be replaced. Google Model A Ford Wiring Disgram and it will come up...Ernie in Arizona

[Hipopinto]

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Than you for all the help!

I look forward to figuring this out

Dave

[chrs1961815]

I have a feeling it has to do with the age of the wire. The wire make look okay but the insulation is most definitely dried out and most likely fallen off shorting the wire out. Been down the road before chasing problems with old original wire. You will continue to have shorts unless you replace the whole harness. It is an insurance policy too on the car.

[1crosscut]

If it's not blowing immediately perhaps it's your brake switch shorting out when you first step on the brake.
Easy to have that happen and not notice the connection between the two right away.

[Hipopinto]

I will start looking today

Thanks guys

Dave

[nkaminar]

This is a good site for all things electrical: https://www.mafca.com/downloads/Semi...ex%20Janke.pdf

[rotorwrench]

The majority of the load circuits are directly connected to the generator or alternator. The amp meter line that eventually makes it back to the battery runs from the gen/alt up to the terminal box.

If it stopped blowing fuses after the gen/alt disconnect then the horn and lights are likely involved. A protective device such as your fuse is there to protect all the wiring, Fuses blow immediately under direct short to ground. They blow slowly when there is either some loose wiring or some kind of intermittent shorting such as the horn use or brake light function. Loose wiring connections can cause resistance heat build up localized to the loose area but wire damage can happen due to the heat build up.

An alternator has a diode bridge inside to prevent reverse current flow back into the alternator after shut down much the same as a cut out does for a generator. A bad diode in there can cause problems as well.

If you want to learn about auto electric, the model A is the best and simplest way to start learning. Study the MAFCA diagrams in the link above. The only thing I've ever questioned about that link is the way the photos show the amp meter to be connected. In one photo it looks backwards to me but that would only cause it to indicate backwards. The load should be connected to the charge side of the amp meter. Discharge is normally connected back to the battery. This would change if a car was wired with negative ground but the model A is suposed to be positive ground,

[Hipopinto]

Thanks guys

I will figure this out

Dave

[Chris in WNC]

new wiring harness is inexpensive and easy to install.
drop the fuse size down to 20A.

[Hipopinto]

Where do you buy a complete harness?

[chrs1961815]

I would buy it through here. They are a pretty good supplier of stuff.
https://www.snydersantiqueauto.com/

[rotorwrench]

The wiring generally comes in separate pieces with the lighting & horn being the largest part assembly due to the light switch connection for all that. The wires to the terminal box and the under dash wiring are separate pieces. The headlamp wiring was internal for OEM lamps with bayonet connections of the conduits. The dash light is a separate part as are ignition & coil hot wire. A cross over for a dual tail light or for cowl lamps are separate pieces. A Sedan type car may have a dome light and that would be a separate assembly.

If a person has an original Electro-Lock pop out ignition switch then it is a unit part with the breaker wire. If you don't have an OEM pop out then the ignition switch wiring generally has to be modified to either turn the power to the coil on and off or to open and close the ground circuit to the distributor breaker points.

[Hipopinto]

Thanks for all the help guys

When I get home this weekend I will find out what’s happening

Dave