Hey, im a complete newbie to this, but with my 73' 280s on the passenger side behind the light there is a resister with a white box thing over it and it has 2 tweminals on it, it think it is part of my imobiliser system, but i had similar problems and i tracked it down to these terminals.... all they needed was a clean and i havent had this problem since! hope it helps!

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73' 280s