Ignition light and battery

[Gargrav]

Hello all
I'm hoping that I can get some info about the problem with my Stag 1970 mk1
When I remove the keys from the ignition the ignition light will come on after a while and then after a couple of days it will drain the battery.
I have run the car and removed the battery terminal and the car still runs it is showing charge on the gauge.
Any ideas has anyone else had this problem?

[dasadrew]

This post was just discovered in the TECHNICAL GUIDES DO NOT POST REQUESTS FOR INFORMATION IN THIS SECTION section.

Moved now to main forum where someone might be able to help out.

Drew

[StagJonno]

Sounds like a faulty diode in the alternator, though as it's an early car fitted with a separate regulator (mounted to a suspension turret, drivers-side in the UK), that could be the problem. Am afraid my last dealings with a separate regulator was approaching 50 years ago and the details escaped long ago .

[trunt]

Try disconnecting the alternator, if it keeps the charge overnight then thats probably it---a leaky/faulty diode, but again I'm not sure how the external regulator could affect this.

Terry

[wilf]

Don't leave the car with the battery connected. Alternator faults like this can cause fires.

[v8ken]

You might be able to get away with this kit if you have one of these alternators,,I did.Ken,
-https://www.ebay.co.uk/itm/172722148546

[DZP]

What does the voltmeter read with the engine running?
I suspect it will be up at 16v because the transistor in the Alternator Control Unit is permanently shorted to ground and there is no output control of the alternator.
Normal operation:-
Ignition on, engine start, alternator generates AL output to energise Alternator Relay, 12v fed to F+ on field coil, alternator relay connects F- field coil to earth, alternator output rises, ignition lamp goes out.
Voltage rises about 14.4v, Alternator control + feed turns the transistor off, F- field coil is disconnected from earth, alternator output drops.
In your case you have some form of earth on the F+ field coil side of the Ignition lamp and hence it illuminates.
I expect the Alternator Control Unit has a smoothing capacitor for operation of the transistor and hence that is why the Ignition lamp illuminates slowly after turning off the Ignition.
I guess it might be possible you have a short on the field winding brushes or slip rings.
So, if you have over 14.4v displayed with the engine running, I would look first at the Alternator Control Unit, making sure the + connection has good contact.
I hope that helps.
Den

[StagJonno]

Meant to add in my original reply, it's a very bad idea to run the alternator without the battery connected - you can get high voltages, enough to cause further damage to the alternator diodes as well as knack the radio etc.

[Neil in Deal]

Mornin' all,

Agree with the others regarding ever running with the battery disconnected, the high(er) voltages can cause all sorts of damage, including overheating wiring.

I had a bit of an experience with a Mk1 VW Golf, when it was less than a month old.
We were up the West coast of Scotland, and literally as we arrived at our overnight B & B the alternator warning light came on.
Quick look under the bonnet, drive belt ok, but "a bit of a smell", a very HOT smell. Worrying.

Set off for home, alternator light still on, Smell inside the car becoming stronger.
Arrived home, lifted bonnet, to be met by VERY strong "burning" type smell......and a partly melted battery! (Yes, I know I should have stopped earlier....)
Luckily it had just deformed and had not split open. Immediately disconnected BOTH battery leads and phoned the supplying dealer to whinge/request they attend with new battery and to check out the alternator.
When they arrived (in good time, credit where it was due!) my suspicions were confirmed. Bit of a clue when the technician unloaded a new alternator, belt and battery from the van.
Our car was the 3rd one they had been called to that week.
It appeared there was a "rogue batch" of alternators fitted to Golfs. The built-in regulator/diode pack was failing, causing continuous over-charging and melted batteries.
Not only was it causing breakdowns, but also one car DID have the battery go into full "meltdown", making a huge mess under the bonnet. (Plus the dealer was having to source replacement batteries in each case, as they had to be presumed to be fatally over-charged.)

So, if in doubt - disconnect the battery COMPLETELY.

Stay safe,

Neil.