Help Please - Engine cuts out when Boost Starter removed


I’ve just been to see a little 2003 MX5 which is a little untidy but it would be a winter project BUT

It’s been standing for 9 months and I was told that the “Alternator was faulty” however, when you turn the ignition key, no dashboard lights.  Connect a “Booster Starter Pack” and all lights come on and the car fires up and runs just fine
HOWEVER . . . . . 

When you disconnect the Booster Starter Pack, the engine dies and there are no dashboard lights.

I always thoughtt that once started, a car doesn’t need the battery connected? Or is that just on old Morris Minors? :wink:


could anyone advise what this fault is likely to be please?


PS. When the engine is running, the “Battery Symbol” light and the “ABS” light on the dashboard, stay illuminated

At the risk of stating the obvious, it sounds like the alternator is shot. The battery light is indicating that the battery voltage is low and should go out as the alternator pushes volts into the system (typically a bit under 14v). 

Most likely, the battery is fully discharged, hence the need for the booster pack. The booster is obviously fully charged but once it’s disconnected, there is no battery reserve power or alternator generated power to keep the spark plugs and ECUs supplied with the current required to keep the engine running. Simples.

ABS light could be unrelated to the underlying electrical supply problem.

It probably needs a new battery too, if it’s been standing in a discharged state.

Thanks Barnsley Rob, that sounds perfectly feasible.

I guess things have moved on since the Moggie Thou



You definitely answered your own question with your original post 

even the morris needed voltage to run :slight_smile: