Link between horn and lights not working and no spark.

[Cornishman]

I have a 31 Sports Coupe with two bulb headlamps. I drove my car outside yesterday, stopped it and with my son's help looked at making sense of the lights. At that point; the horn worked, the stop lamps worked and the headlights would light in one position and the parking lights in another. The rear lights weren't working. Having seen the headlamps work I went to see if I could 'feel' the switch engaging in the position that wasn't working. At that point everything electrical stopped working except the starter. The engine cranks over well but the horn and lights have stopped working and there is no spark at the plugs or when the contact breaker is opened. All this is more confusing as there is over 6.5 volts everywhere there should be. That makes me think it's an earthing problem. Am I correct? For example the horn receives power but does not work when the button is pressed.
Can anyone think of a fault that stops the lighting circuit and the ignition working even though they have power?
If the starter wasn't working so efficiently I would think it was the earth terminal from the battery that was at fault.
I have followed troubleshooting guides for the ignition but can't believe that its failure is unrelated to the lights and horn.

[Tom Wesenberg]

The power passes along a single line from the starter switch through a fuse, if you installed one, to the terminal box, through the ammeter, back to the terminal box, to the coil and another wire to the cutout, where the horn/lights terminal is fastened.

Each item has it's own ground, so you'd have to loose a lot of ground points at the same time for this to be a grounding problem.

It's most likely a problem in the terminal box or ammeter, such as a loose or dirty connection. It sounds like you have voltage, but not enough current flow, which can happen with a loose or dirty connection. Clean and tight will make it right.

[Cornishman]

Thanks for that. It's such a simple electrical system it shouldn't be too hard to sort it out. I have a new dashboard wiring loom and ammeter ready to fit so it sounds as though it might be worth fitting those first. The car already has a new terminal box and that was fine before now. I'm always worried about doing too many things at one time as it's easier to correct things when they go wrong if you've only changed one thing at a time.
Luckily I'm still waiting for the paperwork that I need to get the car registered so all the work I'm doing isn't stopping me from driving the car!

[Mark W.]

I have a battery that was cooked by my generator - it gives a full 6+ Volts, but does not seem to have the amperage to fully light my dash lamp but if I look close the wire tries to glow. This might be a rarity, but that's what happens when a generator goes haywire. Pretty soon I'll have a rebuilt generator with a tight third brush...

[Mitch//pa]

Here is everything you need:

[Redbird]

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Disconnect the battery when replacing wiring harnesses.

[Tom Wesenberg]

Originally Posted by Mark W.

I have a battery that was cooked by my generator - it gives a full 6+ Volts, but does not seem to have the amperage to fully light my dash lamp but if I look close the wire tries to glow. This might be a rarity, but that's what happens when a generator goes haywire. Pretty soon I'll have a rebuilt generator with a tight third brush...

It sounds like your dash light wire is grounding out. Check it for frayed insulation, or pinched in the edge of the instrument panel on later models.

[Cornishman]

Originally Posted by Redbird

Disconnect the battery when replacing wiring harnesses.

That's what it says in the book too.

[Cornishman]

Just an update. I replaced the dash wiring and ammeter and the car started straightaway. The horn works too. I haven't checked the lights yet as I'm going to replace the wiring first as it is in poor condition.

[mshmodela]

In addition to what TomW mentioned, does/did your ammeter get warm/hot? See middle of this page:

http://www.mafca.com/tqa_electrical.html

I've had some electrical issues and early this season noticed mine was getting very warm and noticed a LOT of moisture in the ammeter... I checked the connections and made a very small pin hole in top of my ammeter (on the back side) and dried out the meter with low heat gun... The ammeter no longer gets hot and so far no electrical gremlins have returned.

[burner31]

Seems a Model A would be a very rare sight in France.
Hope you have strong arms...everyone is going to be waving at you.
Have fun