You really need to have somebody hook a Tech II to it and scan for codes, if the security light continues to flash there has to be some code being returned.
I don't think the flashing security light, and the gauges problem are the same issue, unless somehow they are grounding each other out.
I do not have access to a diagram atm, so I cannot provide much help as to tell you where to check to see if there are any ground problems.
Other than to check your battery cables for corrosion, if there is any corrosion clean them, also try to check your ground buss for corrosion.
I am not sure if it is in the same location as the 92-99'* were.
So this link below may not apply to you, but I am sure somebody will post, and be able to help you a bit better as to finding that ground buss.
Ground Buss Corrosion 1992-1999