The clue here is the heater and headlamps causing the car to die. Check your alternator, if it can't cope with all those accessories switched on (it should be able to) the system voltage will drop and then,

1. The Abs computer will shut down and bring up the warning light

2. The ignition will become weak and the engine die.

I don't think this one is anything to do with the OVP relay as this has nothing to do with lighting or heater circuitry.

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Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)