RRC headlining

I've recently purchased a number of trim fixings (MWC8228LG) in order to remedy my '87 Classic Vouge's slightly drooping head-lining, but before I start making holes can any one advise me as to the likely location of any wiring above the backing board, especially at the rear of the car. I know the only long term answer is having a new head-lining fitted, but I'm trying to delay such a large expense for a while.
Thanks in advance folks.

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