electrical/charging gremlins

[realslimshady]

I just replaced the ignition switch on my circa 1970 A25 with original AB21 engine, and now have problems with the alternator/charging. After lots of fiddling and cleaning of connectors the ignition warning light now illuminates when switched on but stays on after starting until the rpms reach about 1500 when it goes out. However, reducing to idle after a couple of seconds it comes on again. Related to this, the hour(?) meter does not start counting until the light goes out, and speeds up/slows down in accord with engine speed, and stops again when the charge light comes on again, is this correct?
Any pointers as to where to look/test welcome- I'm quite prepared to remove the alternator for testing by specialist but would like to eliminate any wiring gremlins first.
Also possibly related-when the old ignition switch was playing up, the hour meter worked only randomly, but once when it stopped the 'water speed' indicator started working (which it never had previously) stopped working after a while, and is not working with the new switch......

[dkirsop]

The alternator light will come on when the voltage from the alternator falls below 12V. The hour meter typically requires a voltage of at least 8V to work. Is the alternator original, with an old style regulator mounted in the electrical cabinet, or has it been replaced with an alternator that has an internal regulator? Somewhere in the output circuit from the alternator you have a significant voltage drop. Either a diode is blown or there is a poor wiring connection.

[realslimshady]

it has the old style with regulator in the cabinet. working out which wires are in the 'output circuit' is the challenge.

[dkirsop]

I would start with the regulator. Pitted contacts, poor wiring connections, etc. Hopefully the wiring schematic is still attached to the back of the door.

To check that the field current is good when you switch the ignition on, WITHOUT STARTING THE ENGINE, hold a screw driver to the alternator pulley shaft. There should be a strong magnetic pull. With the ignition off, there should be no magnetic pull.

The next step is to measure the output voltage at the alternator when the engine is running. Connect the positive lead from your voltage meter to the alternator output and the negative lead to a good ground. You should get a reading between 13.5 - 14.0 Volts.

A strong magnetic field and good output voltage are signs that the alternator is o.k. and the problem lies elsewhere.

[realslimshady]

thanks for that-I will try the magnet thing next time I'm there.
I have just returned from having another go- I replaced the spade connectors to the ign warning light, removed and cleaned as far as possible the three pin connector to the voltage regulator, and its twin at the back of the alternator, and also disconnected and cleaned the two main feeds on the back of the alternator.
Result-now the charging light stays on constantly! I did put a voltmeter to the back of the alternator with engine running but only got battery voltage, however when I tried at the 'made' relay below the regulator I had 17 volts....I really can't get my head around the wiring diagram and those two relays...or how I'm managing to make it worse....

[tribologist]

I wonder if it would be easy to fit a 1 wire alternator like the Delco 10si that you can find at any car parts place on the planet. I fitted one of thise on my old -67 Volvo 1800 in place of the old DC dynamo. Its the go-to alternator for old tractors and farm machinery. It only needs one 6-8awg wire over to the battery terminal on the starter. Its probably cheaper than a regulator. The Bosch alternator used in the old Volvos are certainly more expensive ~$200+) than a 10si ($30-60) and having a alternator rebuilt is not cheap either.

Ulf

[realslimshady]

well that's certainly an interesting idea-but what happens with the rest of the wiring? (to the charging light) I'm quite happy doing electrics but would need guidance over which components would be made redundant.
Not 60 bucks in the UK either- 100 quid, but if it's a long-term fix....

[tribologist]

Maybe there is a low cost alternative Lucas alternator... The Albin motor parts diagram shows a DC generator on the 21 engine. Maybe it has been replaced in the past. The 10Si has three connections. The main output stud that you connect to the 12v on the starter, a exitation lead that you can simply connect to the stud and then a charging light. The charging lights other terminal goes to ACC on ignition switch.
Here is a nice write up.
http://www.oldengine.org/unfaq/10si.htm

I might go that same route if it turns out being an issue having a 40A alternator charging my two group 27 house batteries and a group 24 start battery. I hope not but we will see how it handles them when they are low on charge.

Ulf

[tribologist]

What model alternator and regulator do you have now?

Ulf

[realslimshady]

Ulf- there is a handwritten note on the wiring diagram saying 'Bosch 0 120 400 614. No idea about the regulator.
I have an old Mitsubishi Shogun alternator l just dug out of my shed. Assuming it physically fits, is there any reason it won't work? It has two spade connectors for the exciter coil and charge light as well as the main connection.
I'm struggling a little with the wiring diagram-which of the original wires is the 'exciter' one?
Or, if l follow the suggestion of earlier, i.e connect the exciter direct to the main 12v feed, will that be ok with 12v supplied constantly all the time the batteries are on?

[Tree]

Ulf- there is a handwritten note on the wiring diagram saying 'Bosch 0 120 400 614. No idea about the regulator.
I have an old Mitsubishi Shogun alternator l just dug out of my shed. Assuming it physically fits, is there any reason it won't work? It has two spade connectors for the exciter coil and charge light as well as the main connection.
I'm struggling a little with the wiring diagram-which of the original wires is the 'exciter' one?
Or, if l follow the suggestion of earlier, i.e connect the exciter direct to the main 12v feed, will that be ok with 12v supplied constantly all the time the batteries are on?

Pop over and have a chat with Terry Donovan at Donovan’s auto electrics. He can also test the alternator etc. Although he’s mainly auto electrics he has his own boat and knows his way round a 12 volt system. He’s also very keen on prices.

If you want a coffee while you’re over that way I’m just in the Sanderson Centre.

[realslimshady]

do I ask for 'tree' at the sanderson centre??

[tribologist]

That Bosch number is for the alternator itself. You can not hook the exitation to 12V. That would probably burn up the winding in the rotor and overvoltage your electric system. There might be a combined brush holder/regulator for that alternator. A good auto electric shop would help on that.

[Tree]

do I ask for 'tree' at the sanderson centre??

Hahaha drop me a PM and i'll give you my details.

[realslimshady]

removed alternator and stripped it this evening-one of the brushes completely knackered and the matching slip ring similarly so-replacement on order. At least I know all the wiring connections are good now And I replaced the ancient metal box relays with new ones so they're good too. Will update once new alternator fitted.