Battery going Dead When ign switched off

Help Please.
Just got gti through its mot today after being sorn since October.
I charged the battery up at work as my smart charger at home said it was dead and whould not charge it up.
No dash lights nothing.
Charged the battery not a problem at work , took for mot passed but the volt meter said 11.5 when driving along.
When i got home the digital clock stayed on when i took the keys from the ignition.
Also noticed that the red oil light was very dimley lit and continuted to stay on with no key in.
Does anyone know what the reason for this.
I was thinking alterntor or ign switch.

Paul

Ignition switch is first suspect, ground and or cluster exciter wire is another, and I would take my ride to the parts store and have them test your alternator… Did I also mention Grounds?

The 11.5V is a sign that you aren't charging the battery from the alternator.

Lights that stay on is usually an ignition switch that is flaky, so I think you have 2 issues possibly 3 as the 3rd is wonky grounds.

Have a look at the alternator regulator, if the connection are corroded or the brushes are worn get a replacement, there's 2 screws which hold it in..

https://www.ebay.co.uk/itm/VW-Golf-MK1-MK2-Scirocco-Caddy-GTI-1981-1992-Alternator-Voltage-Regulator/163583779808?fits=Model%3AGolf&epid=249110080&hash=item26165a63e0:g:-qcAAOSw3qVcm-z~

How old is your battery?
could be the battery is at the end of its life if your smart charger would not charge it…..

Forgot to add you may want to check for a parasitic drain.

How To Perform a Parasitic Draw Test - EricTheCarGuy - YouTube

rectifier i think putting battery
light on  with ignition off

probaly wrong again but
how is a local parts store
going to do more that you
could check yourself at home

Over here most auto parts stores will test the alternator on the car, or you can take it off and take it in to the store.

how do you test an alternator
on the car surely using a volt
metre how many part stores
have the equipment to test it
removed from the vehicle
luckily we do have a vice a
motor and and v belt to check
the output