With winter just around the corner, and only doing shortish journeys most of the time, I was thinking about investing in a block heater for my '85 500SEL (117.968).
I understand that the same block heater fits pretty much all Mercedes from the late 60's up to 1992 or so.
When I had my engine out of the car, I cant recall the big plug with an hex opening that the block heater would screw into. Can anybody tell me whereabouts it is on my engine?

Also, being a V8, are there two of these openings, and is it worth installing two heaters?

Thanks.