Starting circuit challenge - intermittent fault SOLVED
Ballast resistor has nothing to do with starting.
Your Australian Valiant is not quite the same wiring as a '69 North American build.
But other than some insulation color and attachment locations, its works the same.
Car can try to start, but turn key again and nothing. then later it will work again.
Interesting discovery is the the HORN works all the time.
Assuming you've removed the battery terminals and made shure they are clean and snug....
Do you have a voltmeter?
Attach it to battery and place it where you can observe it while cranking the starter.
When the key is in Start, the ammeter (in your instrusment panel) should show about 5 amps discharge.
That's power going to the ignition, and to power the starter relay.
The voltmeter should show a slight drop in available voltage. When starter solenoid and starter engage the battery voltage should drop noticibly. But if goes below 9.5 Volts - the battery is weak.
So power is getting to the horn but sometimes not reaching other electrical components.
at the same time no dash lights, no interior light and no headlights or tail lights.
Interior lights, tail lights, and dome light are on a fused circuit.
The headlights are on a circuit breaker inside the headlight switch.
Assuming you're not seeing the ammeter indicate discharge (which would be a short).
Then there is a break or loose connection between the starter relay and the mainsplice.
Check the connection and wire from the starter relay to the fusible link, the fusible link itself, the connection through the firewall, and if those are all good, then the connections on the back of the ammeter.
I noticed in the wiring diagram that the horn is connected directly from the starter relay, so is one of the first items to get power
Yes. And to add to Murray's comment, the power goes to the horn relay. Inside the relay it connects to the wire going to the horn button. When the horn button contacts earth, then the relay's electromagnetic is powered and switches the relay on. The power now flowing through the horns goes to earth at the horns.
Thought it might be an earth issue, but the horn works when everything else doesn't, so horn is still getting an earth.
And fuses must be OK because eventually I can get it to start again.
The fusible link is a special 16 gage wire meant to fail before any of the 12 gage wires. It could be weakened, or any of the connections in that line could be loose, corroded or otherwise weakened.
Weak connection will still show voltage and allow some power through but choke when there are higher flows of electrons.
Based on your description, I'm leaning toward loose connection in the battery feed (starter relay to main splice) or damaged battery.
