jump-start underhood posts

i have an embarrassing dilemma. The battery in my 1985 928S has gone dead and I cannot locate the under-hood jump start points. I have seen an online diagram, and I know the positive post has a plastic or a rubber cover, but I cannot locate it. This is as embarrassing as it is frustrating. I will appreciate any help. I have a very powerful portable charger to use, as I understand that jump-starting a 928 from another vehicle may not be a good idea. Thank you . . . .

The hot post is at the 14-pin connector at the right front (passengers side) of the engine compartment. That connector is for the engine wiring harness. The bolt that holds the connector to the unibody has battery voltage all of the time. Positive lead goes there. I use hardware at the strut tower for ground.