New battery, alternator, dashlight bulb - poor charge

[T100SS]

My 71 Travller had an alternator when I bought it. It worked fine through two winters, but starting first thing began to get a touch lazy last autumn. I tightened the fan belt and it picked up but soon worsened again. I tested the battery before any use first thing, then the voltage drop as the starter was turned, using an analogue then a digital voltmeter. I then checked the charge, using the same equipment plus the on-board ammeter. Only charging whilst running showed any deficiency at slightly over 12 volts.

I checked all the connections - even on the ammeter then stripped the alternator and cleaned it up with WD40 and clean rag. No improvement, so I took it to a battery shop whom I've never had a bad battery from in about 30 years and several cars and bikes. They diagnosed battery so a new one was fitted.

In no time we were back to square one, but in the meantime various other malfunctions had me dismantling the dash (heater). I broke the charge circuit warning bulb but ignored it as unessential - after all it was merely a draw on charge, not a cicuit compnent (?)

I read somewhere on line that this had to be fixed as without it there was insufficient stimulus for the alternator to kick in (or a theory to that effect) but a new bulb made no difference. It is fine once it has been started and starts eagerly. But it was going quite flat now and required charging almost daily.

Some months down the line after a clutch debacle (now yo know why I hate this car - I can't get this fixed because that is broken and so on) I took the warrantied battery back (plus car) and they diagnosed alternator. I got a used one from a breaker I trust but this didn't cure it. So we bought a new alternator (I could take the used one back but you get fed up of exploring an ocean of used therefore suspect parts). No improvement.

So I went to two different indpendant car spares people and had the battery tested. They both confirmed battery fault but only just - at the moment they were about to remove the tester the reading weakened, whatever.

The battery shop said bring it back, we'll check it and replace it; which is precisely what they did. They said they couldn't find a battery fault. But it is still losing charge over night and starts more by luck than anything. Any ideas?

[bmcecosse]

Well - you say it is ok - but 'just over 12 volts' when running. This is NOT right - it should be 13.5/14 volts when running - it must maintain that when you put on the headlamps and the heater fan...all at decent revs - not just at idling. Can you run that test and come back? Does the IGN light now work - comes on when you switch on, and goes out when you start the engine? My own Trav works fine without the light - but other alternators do seem to need it. Does your OIL light also work as it should - sometimes these get mixed up.... You also need to check for any overnight drain - a simple way is to disconnect the battery overnight - and then see if it starts much better in the morning. Better is to take a battery line off - put a milliammeter in series between the battery and that line - and check for any drain current. You may not have a suitable milli-ammeter for that test - but you can also watch to see if there is a tiny 'spark' at the battery terminal as you touch the line back on the battery. There should of course NOT be a spark. Do these tests and come back to us!!

[blues2rock]

Be sure to check the engine earth strap for a good clean connection at both ends.

[alexmcguffie]

There's a good chance it could be failed diodes in the alternator. Most garages wouldn't have a clue what a diode is and would point straight at the battery.

[bmcecosse]

I think more than one alternator has been tried..... Any progress to report on this problem? Seems to me it can only be an overnight drain - have you tried disconnecting the battery after a good run - and then reconnect in the morning, to see if it turns over better??