Alternator; not charging; no warning light
 

Hello,
concerns Daimler double six (V12) 1979.
My battery is was not charging and there was no warning light telling me about it...
At turning ignition on, a "battery light" is flashing one second and thats all.
The workshop manual is referencing to a Lucas alternator with a connector at the back , but I dont see any connectors. Just 2 or 3 wires. Anybody a clue on how to debug that one and in case necessary (in order to check the diodes and brushes), on how to remove the alternator, which is almost unaccessable . Many thanks.

On that alternator you will have LARGE wires under a nut, they are battery LIVE.

There is a smaller wire that simply plugs in. This is the "exciter" wire, and is in conjunction with the red charge light on the dash. Unplug it, turn ON the ign, and measure the volts in that wire. It should read battery volts or very close. If NO volts, the alternator is not getting excited. It will "self excite" when a certain revs is reached, but idle charging is basically zero.

Not sure on the S3, but on the earlier cars that wires volts was determined by the bulb in the dash being operational, so maybe you got a blown charge light bulb. I know you mention a Red light coming on, and then going out, but as I said, I am not that familiar with the dash layout of the S3, but I doubt that is the bulb I am thinking off.

Removal is simple enough, TIME consuming, and it comes out through the TOP.

some tests done
 

Hallo frends, done som tests
The red lamp that blinked on the dashboard for a second was the coolant t° chacklight, not the battery light. Sorry for that.
tests:
no slipping belt; altern. turns well.
ignition on only:on exitation wire not connected to D+: 11.94 (batt=12.34)
ignition on only:on ex wire connected to D+: 11.81
following tests with engine running 1500 RPM:
battery: 12.44; B+ 11.92
disconnected exit.wire and I have put an AMP meter between D+ and B+: 0 amps (and mA)


Since there is some oil in the region I thought of cleaning with methanol and do the tests again.
What do you think of it

Wont do any harm, but I doubt it will fix it.

Sounds like the alternator is in need of rebuild.

The brushes may be worn down too low, common enough, or the regulator is dead.

The diodes are not a common issue in the big scheme of things.

forgot to mention: battery warning light
 

battery warning light comes ON when I make a mass contact with the disconnected exiter wire (Ignition ON). So this circuit is OK; Brushes or rotor??
Or do you see other possibilities

Bushes are the most common, followed by the slip rings, the then regulator unit.

Lucas regulators were not known for their reliability.

a short on stator resolved; quid regulator checking
 

Hello, I found a short on the stator wiring near where itt was soldered and could repair it. Now the measuring values of the diodes is OK after repair. Before I mount the alternator A133-75; 24102D) I would like to check the regulator.
Anybody has a clue on how to proceed. (It has 3 wires (rd/bl/ye) and of course the body of it which is connected to one of the brushes.
Another question. How can the warning light turn off (with ignition on) after a second or so.

Here in the US, most auto parts stores will test it for free on their alt test harness, perhaps you can do the same there. The service manual does have a section on testing the regulator, but i cant recall it.

The exciter wire connects through the alt to ground, and the other end is connected to 12V via the dash idiot light. When ignition is switched on, till the alternator revs build up, the exciter wire is at ground (hence battery light on), and when voltage rises the dash light goes out

warning light: wiring diagram error
 

Thanks warlock for the suggestion. I ll check it here in europe.
I also check the wiring diagram for this car and saw that one side of the warning light is connected to the + after the ignition switch which is INCORRECT. It is wired after the the fuel pump relais. This causes the warning light to dim after one second when the car is not started. I suppose this is done in order to save some energy when only the contact is on and take care of the rotor windings which are not cooled without alternator revs.

The regulator is a common electrical circuit and is typically called a bridge rectifier in E engineering. You can lookup a diagram of a wheatstone diode bridge and that will detail the operation. Pretty much any stock diode bridge that is good for your rated amperage will work. I completely cut out the Lucas regulator once and it worked fine with the bridge. I eventually just replaced the whole unit when the coils failed. I now use a generic Marine grade gm alternator. Haven't had an issue since.