On 01/05/2018 11:15, The Natural Philosopher wrote:
On 01/05/18 10:25, Graeme wrote:

The Morris again.Â* 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.Â* Restarting a couple of hours after a good run, no
problem.Â* 24 hours after a run, battery sluggish but will just about
turn over engine.Â* 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.Â* 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.Â* About the only other electrical
accessories are indicators, wipers and simple on/off heater blower,
but they are wired through the ignition.Â* 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?

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.



+1. A mate of mine had a similar problem once, it turned out to be that
the radio was drawing power even when switched off (and the light went
out properly).