OT ..Madel A started backfiring from turning lights on..advice please

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Model T Ford Forum: Forum 2018: OT ..Madel A started backfiring from turning lights on..advice please
Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Sunday, April 22, 2018 - 06:58 pm:

A friend recently finished a restoration on a 30 Coupe and we went for its first decent test run yesterday.
Was buzzing along great about 45 mph when we turned the headlights on the engine started misfiring really bad with massive back firing etc. We managed to just limp home, jerk jerk backfire, dogs barking and people coming out of their houses....funny.
On inspection the aftermarket Fuse fitted above the starter is blown hence lights, brake lights etc not working.
It has a new wiring receiver thingie at the bottom of the steering column which has some issues as the horn can go all by itself and since the light switch comes down the same system perhaps the horn and this problem are related.
I can understand the fuse effecting the lights etc but what is the link to this and the running of the engine? The problem occurred exactly when the lights were turned on.
Any suggestions before we investigate would be appreciated.
Thanks in advance


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thomas Mullin on Sunday, April 22, 2018 - 08:03 pm:

Kevin, It sounds like there is a short somewhere that sucks the voltage from your system when you turn the lights on.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Schedler, Sacramento on Sunday, April 22, 2018 - 08:27 pm:

That backfiring will probably blow your muffler. Check or renew the light circuit all the way from the switch to all of the lights. It's probably going to be in the switch down at the end of the steering column. It's been a while since I worked on an A


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenneth W DeLong on Sunday, April 22, 2018 - 08:51 pm:

If my wifes A will not start it's because i have forgotten to reinstall the fuse.If your fuse is burned are you running on the gennerator and with the lites on you might have a large voltage drop??Bud.


Top of pagePrevious messageNext messageBottom of page Link to this message  By lyndel butler on Sunday, April 22, 2018 - 09:00 pm:

My model A did that.The headlight was not grounded good.Rust and paint between the headlight and bar they are mount on


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Dodd on Sunday, April 22, 2018 - 09:33 pm:

I have seen fused systems where the fuse is placed between the connection on the starter foot switch and the single wire to the whole electrical system. The problem with this is that with the car running above Idle (cut-out engaged) the charging system looses its reference voltage and will cause a RPM related voltage spike due to not being connected to the battery due to the blown fuse.
I have seen ignition points fry in a few miles of 40-50 MPH driving. If you run a fuse, make sure the wiring harness is modified to only service the lighting system with the fuse!


Top of pagePrevious messageNext messageBottom of page Link to this message  By wayne tomlins on Sunday, April 22, 2018 - 11:17 pm:

My A Tudor did something similar, one of the horn windings burnt out when I pushed the button . The fuse fried [ takes out lights, ignition but not starter] but it still burped & farted 100 yards home. A new fuse & holder plus another original horn motor & running sweet again. I did go thru all connections & earth strap & found a few frayed wires, so check everything, especially the connections behind the dash panel.
Wayne in NZ


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Monday, April 23, 2018 - 01:25 am:

Engine won't run all that well if the generator is trying to pump out amps to charge a battery that isn't there. Replace fuse and see if it runs better. It might be a case of the points being a tad burned now.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Monday, April 23, 2018 - 04:12 am:

Thanks for the feedback guys. I called around today and he has replaced the fuse and the motor runs perfect as long as the light switch is left off.
Its good to see it fixed but the cause worries me, some of the above suggestions will be a help in tracking it down. The wiring is all new done by a local auto sparkie and I wonder if there is a trap that a modern sparkie could fall in?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Miller, Mostly in Dearborn on Monday, April 23, 2018 - 05:56 am:

May I suggest you move this discussion to Fordbarn.com? They have the most active Model A forum of which I am aware.

My first antique car was a ’31 Model A. I still own it. Over the years, I’ve come to know the Model A suppliers well. It is my opinion that Bratton’s has done much for the hobby by making quality reproductions available; in most cases following the print or improving the part with modern materials. Additionally, Steve at Bert’s in Colorado continues to supply good original parts. Mike’s Afordable makes a darn good steering kit but that’s another story. The others also have good parts but it’s good to know what you’re buying.

Assuming your Model A is restored and wired stock, the headlights are probably causing your problem. The “new thingy” at the base of the column holds your light switch spider and the switch body. You mention the horn goes off when you turn the light rod. This is because the contact rivet in the center of the phenolic disc is going to earth inside the light switch housing. This is not a short since the six volts goes directly to the horn first. Disconnect the battery, remove the light switch body by flipping the bail and then look through the large hole in the end. On mine, I put an insulator like a length of large plastic tubing to ensure the rivet won’t contact the steel switch body. If your switch body is bright and shiny, you can suspect that it’s a reproduction. Find an original if possible. Bert’s and Bratton’s are two possibilities. The connections inside the headlight switch are all crimped and soldered, I doubt if your electrician did anything wrong inside there.

Now, the short. It’s probably in one or both of the headlights. I haven’t checked the suppliers recently, but most of the wiring harnesses in the headlights are total crap. If you disassemble your light and find three black vinyl wires, you probably have these harnesses. Where they fail is the white nylon insulators in the connector have large holes and the brass contacts slide off to the side and go to earth, shorting the system. Many restorers cut the three bullet connectors off the lighting harness and then make the connection inside the headlight bucket using wiring nuts. I did this for a while and eventually restored original parts and set it back the way Henry intended.

While on the subject, many of the late style brake light switches are also suspect. This is the one that fastens to the frame, not the transmission.

Finally, the fuse. I bought one and threw it in the tip. It became unsoldered and caused problems. I have yet to see a good reliable one marketed by the Model A suppliers so I made my electrics safe and don’t use a fuse.

One other bit of advice. Assuming your distributor is stock, carry a spare condensor.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, April 23, 2018 - 11:27 am:

The original wiring on a Model A did not have a fuse. Your car would run better if you had the ignition unfused and the fuse only in the light and horn wiring. or use a separate fuse in the ignition system only.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Monday, April 23, 2018 - 08:04 pm:

Thanks Tom, Some great info and will follow all that up.
Norm I see in most model A pics people have fitted a fuse above the starter but what you suggest is helpful.
Just to clarify you don't have to turn the light switch to toot the horn it will toot all by itself sometimes when car is parked up so it has been disconnected at the horn until solved.
The new thingie at the base of the steering rod looks poorly designed with a risk of shorting, maybe the best option is replace via Toms leads.
Thanks again


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Tuesday, April 24, 2018 - 12:34 pm:

The Model A BCM (body control module) is a scary thing. It us a wimpy plastic and metal thing with a bunch of wires sticking out at the bottom end of the steering column.

It is supposed to control the lights and horn. When it goes bad you don't have many options because the contacts on the new ones are not very good and they include a bunch of wires that need to be connected to the correct place.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Wednesday, April 25, 2018 - 12:19 am:

It's been a while since I've purchased Model A parts, but some 10-15 years ago the repro headlight sockets/connecting sockets were made of material thinner than the originals, so, depending on how the maker held dimensions, either the inside or the outside was wrong, usually the inside. The connecting insulator used on the wiring harness connection to the headlamps was too small too, so now the fit is completely loose. To top it off, the metal end on the wire is not the same shape as the original, which are flat on the end to provide a better connection with the lamp wires. The best solution? Find original parts and use them, and modify by grinding & soldering the new harness wire ends to match the originals. Then you will have good headlamps. Remember, the lamps worked fine when the cars were new, the design isn't bad, the repro parts are! As for your horn, the horn tube needs a nice end contact on it, that fits into the spring loaded contact on the wiring harness base, and the wires on the base CANNOT contact the bottom of the metal housing.
I repeat: the system worked well when new, and will when old, if properly cared for and assembled with correct parts.
Oh, and those repro headlight harnesses with the white plastic holders; the white plastic melts when the connection gets warm and then the wires really get sloppy. that insulator needs to be fiber to last.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Wednesday, April 25, 2018 - 06:02 pm:

Exactly what David Dewey said.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Weeds on Wednesday, April 25, 2018 - 06:10 pm:

Thanks guys great feedback.
I'll pass it all on


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