[Mgs] Modern radio in old MGB car

[PaulHunt73]

I can't really see that, even if you had installed a 'modern' computer in your V8.  Radios with a memory will put a drain on the battery, but it shouldn't be a problem after just 'a few days'.  Even modern cars shouldn't do that for two or three weeks at worst.  I had to put a cut-off switch in my V8 as the alarm was draining the battery in couple of weeks, since when it has been fine.  The radio in that keeps its stations, and I've run a bypass feed direct to the clock.  I also had to put one on my 'modern' as it's hardly used in summer and wouldn't start the engine after a couple of weeks.  That loses its stations so put a bypass for that and the clock which conveniently are on the same fuse, but it still fails after several weeks of not being used.

Checking for a drain isn't difficult even if finding the cause is time-consuming.  Remove the battery earth strap and connect a VOLTmeter in its place.  If you have a dynamo there shouldn't be anything shown on the meter.  With an alternator there is usually a microscopic drain from the diodes, which shows up as a few volts on an analogue meter and 12v on a typical digital.  If you see 12v on a typical analogue you do have a drain.  Unplug the alternator and if that drops to zero on an analogue then the alternator diodes are suspect, a digital is too sensitive to tell the difference directly but you could measure the current.

If you still see 12v on either then disconnect any alarm or 'in car entertainment', then the purple circuit fuse, hazard flasher fuse, brown wires from ignition switch, lighting switch, fusebox, relays and solenoid until it drops to zero.  The thing that caused it to drop needs further investigation, of course.

PaulH.
  ----- Original Message ----- 
  ... 
  Then radio man thought that modern radios had facilities that connected them to "modern" car computers and thus the drain as the radio would keep "on" and chatting even when it was turned off. ...
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