Motorhome/auto electrician

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Sorry, can’t help with electrician but if your battery is charged (should be nearer 12.8v) I’d suggest you check  the earth battery terminal - give it a wiggle to see if the connection is bad. If the immobiliser is faulty the engine will usually turn over, but not start.

 

As Bill says, 'pushing out 12v' is a long way from a healthy battery, in fact it's knackered if it's really 12.0v...

het a decent charger on it for a couple of days and then test the resting voltage.

full for lead acid is 12.6-12.8

but even with a 'flat' battery of 12.0v you'd expect the dash lights to light up

Yes, hence my suggestion to check the earth connection.

Why not buy one of those diagnostic scanners they are fairly cheap that should show the codes for any faults 

Earth strap issues very common, good shout.

If you want to check the earth strap if you have some jump leads connect the black lead to negative battery terminal and the other to some unpainted part of the bodywork