Topic: 69 ammeter wiring

[martin]

I am repairing my engine bay harness. The ammeter wiring needs to be replaced. Both wires are no longer connected to alternator and starter relais and are shortened.

Do these two wire's need a certain length and thickness ?

Is it possible that the electrical schematic is not correct ? When i look at the yellow wire going to the alternator it starts yellow from the ammeter and changes into black half way.
When i look at the harness it is yellow all te way (maybe the black parts is cut off).

Martin

[midlife]

I am repairing my engine bay harness. The ammeter wiring needs to be replaced. Both wires are no longer connected to alternator and starter relais and are shortened.

Do these two wire's need a certain length and thickness ? Yes and Yes.  The ammeter is basically measuring a small difference in resistance between two wire sections.  Both length and gauge affect resistance.  The ammeter will still work with wire changes, just not as sensitive.  It's already not very sensitive.

Is it possible that the electrical schematic is not correct ? When i look at the yellow wire going to the alternator it starts yellow from the ammeter and changes into black half way.
When i look at the harness it is yellow all te way (maybe the black parts is cut off). I can't be sure what you're stating, but it is most likely yellow all the way to a certain point.  Part of the wiring for one ammeter line is 12 gauge (the black part, IIRC) and the yellow picks up from a factory splice point.  The red wire typically goes all the way to the starter solenoid ring connector. 

Martin

[martin]

Thanks for the reply.

What dou you mean with IIRC ?
This is the schematic i was talking about

As you see the yellow wire changes into black at a cerain point. I would like to know if this is correct and what the original wire lenghts should be.

I hope anyone can check this for me

[martin]

I guess i figured it out looking at this schematic http://www.allfordmustangs.com/forums/classic-tech/544385-ford-ammeters-testing-making-them-useful.html


The pink wire represents the black wire at my schematic and is probably a splice in point onto the thick black/yellow wire.
Now i need to find the correct wire type (resistand wire).

Any info welcome to clear this puzzle.

[midlife]

My examples show that wire to be black, approximately a 12 gauge wire.  There's a factory splice near the starter solenoid: outbound it is the black thick wire and a 18 gauge yellow wire that goes to the voltage regulator; on the inboard side, it is the black thick wire and a red ammeter wire.

[martin]

At the original schematic there is indead a splice point next to the starter solenoid. The wire going to the regulator is shown as a green/black wire.

When looking at the schematic from the allfordmustangsforum
I believe the splice from the pink with the yellow wire is the point where i drew a circle with a question mark at the original schematic, because it is not clear to be a splice point.

So there are actually two splice points ? I may be wrong because i have no complete wire harness to check.

[midlife]

Yes, there is a factory splice point further down away from the starter solenoid.  It contains the black power line on the starter solenoid side and that same black power line plus the yellow ammeter line on the inboard side.

[69cobrajetrugae2]

When a non tach car is converted to  factory tach, why is the amp light disabled?

[midlife]

When a non tach car is converted to  factory tach, why is the amp light disabled?

The non-tach car has an ammeter.  The conversion to tach causes a replacement of the ammeter with an alternator indication light.  When I do conversions, this indicator light will work.  The conversion for the light requires a 15 ohm resistor wire, which most hobbyists do not have access to.  I had to special order 2000 feet of it for a very high price such that my conversions are correct.

[69cobrajetrugae2]

Thanks Randy!

 If you could explain the nuts and bolts of how the light aluminates when the voltage and or current potential across the circuit indicates a no or low charge condition that would be great.

Our 65 fastback has a intermittent overcharge condition which I think is a missing ground or a bad regulator.  The other night the amp light came on then went off upon restarting the car. My voltmeter was not with me but I have seen it in the past go from 13 to 16 volts, the battery side of the coil trails it by 3 volts.


Can a  overcharge condition cause the amp light to aluminate? Can a bad battery cause the car to overcharge?  Thanks!

[midlife]

I once spent about 1.5 hours trying to understand how that system worked and posted it I think on this forum.  I promptly forgot the exact details.  Voltage regulators and wiper motors are my weaknesses.

I believe the light will only work if there's a difference in voltage between the alternator output and the ACC/RUN voltage in the underdash area.  Now before you think "aha!", the light bulb needs something like 8-9 volts difference across the filament to be visible, so the overcharging condition you mentioned would not be sufficient.  The resistor wire is there because if the bulb burns out, the VR still needs a stimulator signal to tell it that regulation is needed. 

The overcharging condition is due to a bad voltage regulator.  Stop running the car now, and replace it with a good quality VR (motorcraft?).  An overcharging battery can explode and do lots of acid damage to sheet metal and other things.  Double check your wires and contacts at and around the VR, as that may contribute to the VR not working right.  Many of those pins are corroded and I often have to replace the pins with new brass ones. 

[69cobrajetrugae2]

Okay good.  If you want a fun read check out the factory low charge warning light circuit on a 1969 Jaguar XKE.

 Jaguar with Lucas, "The prince of darkness" moniker is well deserved indeed.