Lucas control box problem?

[Graeme]

The Morris again. Just to recap, 1968, now -ve earth but still dynamo, control box etc.

Suddenly started to flatten the battery whilst parked, but charges when running. Restarting a couple of hours after a good run, no problem. 24 hours after a run, battery sluggish but will just about turn over engine. 48 hours after a good run, starting by handle only.

I have convinced myself the problem is the Lucas control box, which is almost certainly original. This is a Minor, so there is nothing to be left on when the car is not running, other than lights, which I have checked, ditto interior light. About the only other electrical accessories are indicators, wipers and simple on/off heater blower, but they are wired through the ignition. No radio, heated rear screen or anything like that.

Given that control boxes are around twenty quid, I'm tempted to just replace the old one and see if that fixes the problem, but have I missed anything obvious?

[Dave Plowman (News)]

IIRC, there are contacts inside the control box (a relay) which isolate the battery from the dynamo when it isn't charging. With no fan belt on the car, and charge in the battery, if you make those contacts by hand, the dynamo will motor. And I have seen them welded closed. That would draw considerable current and flatten the battery very quickly. BTW, closing those contacts by hand was a quick and dirty way of polarizing a new dynamo, or re-polarizing one after changing the ground polarity.

But I'd not claim to be an expert on those control boxes - not had one for a very long time indeed. Perhaps 40 years, so likely forgotten what I once knew - if I indeed did. ;-)

[Tim+]

May just be a dud battery. Have you checked for parasitic current drain with the ignition off?

Tim

[Robin]

With apologies in advance if the question's insulting, have you measured the current drawn from the battery to check that that is the definitely the problem (as opposed to a knackered battery)?

[Robin]

47 years in my case; but I still recall the un-joy of trying to clean and then adjust the contacts.

[The Natural Philosopher]

It sounds like you are drawing about half an amp.

I would definitely put an ammeter in the +ve battery circuit with everything 'off' and see.

half an amp is less than I would expect a faulty control box to draw.

I think you should start tracing where that current is going before spending money.

This sounds to me almost like an interior light or similar.

Check what is across the battery that is OUTSIDE of the ignition switch

- typically the headlights and other lights are and courtesy lights and maybe glove vompatment lights.

It isn't the ignition switch as te coil draws about 6-12A!!! and will flatten a battery in a few hours.

I cant see that it can be the control box - if the overcurrent relay sticks closed, then frankly the battery will be flat in seconds of smoke as the dynamo will be a dead short across it.

[The Natural Philosopher]

You needed a decent meter to do that.

[Graeme]

In message , The Natural Philosopher writes

OK, sounds sensible. I do have ammeter and volt meter, standard car 2 inch jobs, although neither are fitted to the car.

I haven't done any formal testing as yet, but am trying to be logical. When parked, I can see that the lights, including interior light, are off. No boot light or anything like that, yet I agree, it sounds just like an interior light fault.

Strangely, the courtesy lights were not working until a week or so ago, when I flooded the door switches with contact cleaner, and now both work, but, if one or both was shorting, the interior light wouldn't come on with the doors open, but it does? With the doors closed, the interior light works using the interior on/off switch, which I wouldn't expect it to do, if the courtesy light switches were shorting. Getting at the rear of the door pillar switches is a bit of a nightmare.

The battery is fairly new (couple of years) and gets little use. Removed from car over winter, and trickle charged occasionally, during the winter.

Dynamo must be working, as the battery is fully charged after a run.

[newshound]

Correct, the boxes are normally openable IIRC (they might be riveted closed) and the contacts are fairly obvious. So easy enough to check before buying a new one. I'm sure there will be drawings on the web.

[Tim+]

Hmm, battery ?suddenly losing charge?. ?Courtesy lights were not working until a week ago?...

Seems to me your fault isn?t too far away...

Tim

[Graeme]

In message , Tim+ writes

I agree. I'm going to follow the suggestion of putting the ammeter between battery -ve and chassis, with everything off, and look for a reading. Assuming there is one, I'll then disconnect the interior light at the fuse box, and see what happens.

[Dave Plowman (News)]

I'd get myself a DVM. That will measure low current accurately. Unlike a

30-0-30 ammeter.

A decent automotive one is worth the extra. Will include a dwell meter for instant checking of the points gap without dismantling, and an RPM function too.

[Dave Plowman (News)]

There are two and three 'bobbin' regulators used. Only the 3 bobbin one includes reasonably accurate current limiting. The MMs I knew had two bobbin types. Three being used on more expensive cars.

[Graeme]

In message , "Dave Plowman (News)" writes

Not a bad idea. Thanks.

In the meantime, other stuff has arisen but I've been for a 20 mile run and disconnected the feed to the interior light. Will be interesting to see how well charged the battery is, 24 hours later.

[DerbyBorn]

?Aren't door pillar switches often a push fit and easily pulled out for chacking?

[Dave Plowman (News)]

Incidentally, worth keeping an eye out for the Haynes manual on auto electrics at autojumbles, etc. Far far better than the normal car manuals. Mine does cover dynamos and control boxes.

[Tim+]

Why not just disconnect the battery for a couple of days? That?ll soon reveal whether it?s a battery fault or something draining the battery.

Tim

[Graeme]

In message , DerbyBorn writes

These are a huge cross head screw, notoriously difficult to undo, 50 years later.

[Graeme]

In message , "Dave Plowman (News)" writes

Sounds interesting, thanks. I do have the Haynes MM manual, and a few others, but will keep a lookout for the auto electrics one.

[Graeme]

In message , Tim+ writes

Yes, that is Plan B. The first idea (as above) should confirm whether or not the interior light is draining the battery, whereas disconnecting the battery will only confirm 'something' is draining the battery.