Quote from: Wittsend on Apr 22, 2024, 12:16 PMThe small dynamo terminal connects with the thinner wire to the control box terminal "D". This is the ignition warning light. The other wire from "D" on the control box goes to the ignition warning light on the dash.
The thicker/heavier wire from the dynamo carries the output (amps) to the vehicle and goes to "F" on the control box.

NO. This is wrong way round.
The thick wire carries the main current (amps) from the dynamo terminal "D" to "D" on the control box.
The thin wire connected to "F" carries the smaller current to excite the field coils.
The charge warning light is a useful indicator of whether it's working, BUT, plays no part in making it charge. (In an alternator system the charge light is critically important, but in a dynamo system it plays a completely different role. Removing the bulb from a dynamo system will make no difference to the charge.)
 
If the wire connecting to the "D" terminal is not thick enough to take the whole output of the dynamo, you run the risk of setting fire to your vehicle.

John

"A" "A1" and "D" are shown as thick cables in the wiring diagram below.

I have the wires connected correctly at the regulator the thicker wire (yellow) to D and the thinner wire (yellow/green) to F. So are you saying that the thinner wire (F) connects to the large spade terminal on the top of the generator and the thicker wire (D) to the smaller spade terminal at the bottom?

Sorry, just would like that confirmed.
And thanks for taking the time to respond.

Other way round.

As Alan Drover says above.
Thick yellow wire from "D" to Large terminal on dynamo.
Thinner yellow/green wire from "F" to smaller terminal on dynamo.

If you were to look inside the dynamo, you would see the large terminal is connected to one of the commutator brushes. The other brush is connected to earth.

The smaller terminal just feeds a small current back into the field windings to strengthen the residual magnetism. Without it, the dynamo would only put out about 2 or 3 volts.

John

Thanks. Sorted then. 

So, I have set it up as described (that's the way I originally had it). However, when ignition is on, the charge light does not glow. How can I troubleshoot that? Thick yellow wire to D. The yellow wire from D (regulator) to the warning lamp. Thin yellow/white to F.

I don't understand if there is no power to D before the engine is started how would the warning light glow. With the ignition on S, there is no power at D or F, and D feeds the warning light.

Additionally, the oil light, which is supposed to glow prior to starting, likewise does not glow - and shows no power on ignition S mode.

Imagine that your charge light is some sort of voltage see-saw. If it is balanced with 12 volts on both sides, then there is no potential difference across the warning light terminals so it will not light.

With the ignition on, but the engine not running, the charge light will come on. This is because battery voltage is coming to the white ignition live wire to that side of the bulb. The other side of that bulb (the yellow wire) is connected to the D terminal of yor regulator. With the dynamo at rest, this is grounded, so the bulb lights.

When the engine is started, 12v from the battery is still being sent to the bulb on your white wire, but as the dynamo starts to generate electricity, 12 volts is also now being supplied from the dynamo to the D terminal yellow wire on the regulator. If you have 12 volts on botn sides of the bulb, there is no potential difference, so the bulb will not light.

I think I've explained that correctly, but not had a coffee yet this morning...

Oil light - simple test, but sort your charge circuit first. Once you have fused ignition lives on the white wires, one will feed the oil pressure warning light. That then connects to the switch to earth. As the pressure increases, the switch breaks the circuit and the light goes out. If there is 12 volts at the warning light on the white wire and 12 volts at the switch you should be able to ground that green and yellow wire and the warning light will illuminate.

Check you have the right bulbs and holders in the right places. All earth to the instrument pack housings with the exception of the charge warning light which must not do as explained above.

Hi,

I have met (caused?) problems by fitting a "ballast type" coil from an S3 ... it was all that Halfords listed.

S3 coils have "double live" input .... one terminal runs from the ignition switch, which is reduced voltage, possibly only 9 volts, which is what a ballasted coil is intended to run on.

The other input terminal is fed from a terminal on "battery circuit", giving a full 12 volts during starting, or possibly less if the battery is struggling to turn the engine.

I assume that the coil, points, etc, do not like running on full 12 volts all the time???

Yet again, my "caring ladies" are demanding my presence, so I will leave it to the Club Boffins to comment on that.


602

Series 3's were never fitted with ballast resistor coils.

With the exception of the Stage One V8 I think.

I don't have a wiring diagram for it.
On the 2.25/2.6 with conventional ignition and negatives earth, a white wire takes the power to the SW (+) side and a white and black goes from the CB (-) side to the distributor.
Opposite way round on the coil for positive earth.

A bit OT, but early Range Rover Classics and the Stage One V8 (I think) had a Eureka wire from ignition to the coil. That dropped the coil normal voltage down to around 10v as the wire was a special resister wire. On cranking, it would start no problem as it got the full 12 volts to the coil, but if the Eureka wire had broken down, you lost coil running power. It would start perfectly then stop as soon as the 12v cranking feed dropped. As the Eureka wire was part of the harness it could not be easily replaced. One Ten V8s ditched the Eureka wire in favour of a simple in-line resister. We just used to fit those resisters to Stage One V8s and early RRCs on an ignition live and ditch the Eureka wire. In the end I upgraded pretty much every LR I came across with a Eureka wire as they were too unreliable.

Triumph stags used a resistor wire as well. Great if you don't know they're there. 70s Harley's used a thinner 'fusible' section of wire  as the first section of loom from the battery to protect the rest of the wiring and my '42 and '54 6 volt Harley's don't have any fusing at all, at least the landy has one 😊

Jon

So did the late MGB's and it was buried deep in the harness. They had a complicated set up of solenoids to switch the coil back to low voltage once the engine had started.