MG Car Repair: red light on dash board wont go out, mgb roadster, ohm meter

Question
I have a 1976 mgb roadster the light on the dashboard wont go out it is draining the battery also touching the handbrake button starts the car thanks

Answer

MGB diode Hi Paul
I presume the red light on the dashboard is the ignition warning light.  Normally this indicates that there is a fault in the alternator.  However, the situation is complicated because when you apply the handbrake the starter operates.

I would suspect that the isolating diode has failed.  I think it is located under the dashboard behind the passenger's glovebox.  I attach a photo of the diode.  Remove it then check it with an ohm meter.  It should be zero ohms one way round and infinity the other way round.  

Another possibility is the failure of the starter relay.  This is located on the bulkhead near the main fusebox.  It could be a wiring fault, so before you replace the relay, check that the earth wire to the relay (plain back wire) has a good earth.  I would use an ohm-meter to confirm this as well.