there is a pretty good FAQ for the water in the trunk at
http://www.240sx.org, look in the FAQ section for "water leak." From what I have seen that is usually, but not always, the problem. For the speedo, I would guess either the speed sensor in the transmission is bad, or the speedo unit in the cluster is bad. I would start with the transmission sensor, cause getting the cluster out is a ***** the first few times. (also you have a good chance of screwing something up cosmetically up if your not careful.) I broke a plastic bezel on the donor car when I removed it. I think there is a FAQ or 2 about the speedo on that page as well.