2.9V Diff between 12V in aft compartment and engine room

I have cleaned ground connections at both ends of the negative cable in the aft compartment; 500grit than 1000 grit also used Deoxit S5 on both terminals of the 12V battery. Cleaned the positive terminal too the same way, and yes the posts too. Everything looks clean and solid back there. Once you are past positive terminal connector are there any other connections in that cable till you get to the jump point in the engine room or is that one continuous cable?

As to the discussion on greasing electrical connections/automotive sockets, I think the idea of a light dielectric grease is probably a good idea where the connections can "bite" into each other pushing the grease out of the way at point of contact but allowing the grease to remain around the connection to keep moisture and the associated corrosion out. These tend to be lower current applications, up to a few amps. On battery terminals I think you want clean surfaces with lots of contact area so no grease IN the connector initially. But once you have a physically solid connection you could apply grease around the outside of the connector/post assembly and form a nice seal which is probably great. A more durable solution but, possibly harder to apply, would be "liquid electrical tape." Liquid tape drives solid but flexible and so would also not have dirt and dust get stuck in it like gooey grease would. I have used Liquid Tape on boats which are generally in a much harsher environment than autos, unless you try and drive under water. It is annoying to have to clean that stuff off when maintenance is needed but that is true of grease too. With the Prius, the battery is so well protected I think this is not too much of an issue.

Now, on outer perimeter lighting connections, I think the grease idea is great because those areas are much more subject to moisture intrusion. And once in the housing, the moisture may hang around through many heat/cool cycles which really causes problems. The grease can offer valuable protection in this case. The grease may add some parasitic resistance between the socket and the bulb pins but I think this is outweighed by the protective properties. Then again I am thinking of traditional marker and mast lights and automotive turn signals, brake lights etc. These new newfangled halogen head lamps might suffer from that parasitic resistance and build up too much unwanted heat at the point of connection causing the grease to liquefy and migrate out from where you want it (or maybe worse). That would be a bummer. I 'll have to study the Prius headlamp connections before I say whether I think grease should be applied there. I'll do that this weekend since I will be doing a bunch of other stuff on the Darkstar.

This is off topic but I have been meaning to ask, is it just me or do the backup lights on the Gen2 Prius seem "not very effective?" (this is a family show)

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It probably means Toyota figures it is not REALLY needed. DIY maintainers tend to "go the extra mile" when doing a job because they don't usually want to do more often than would be absolutely needed* and want to do it better than "some guy at a shop who does not love my car the way I do." Toyota does seem to use connectors with better splash ratings than other manufacturers and I have not _yet_ found one that seemed to be under rated for the current it carries.

It also might just be that the more modern automotive and industrial connetors are better as resisting moisture than those connectors on cars from the 50'-80's that many of us older gas bags (Olde Farts) grew up learning to maintain. And old habits that proved beneficial die hard.

*With a couple notable exceptions on this board.

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