Driving today with the fuse power insert in the airbag slot (and thus running through the ignition), I'm getting much better numbers on the gauge. Idle is still low, at around 5-8psi (once car is warm, but it isn't triggering the OEM oil light)), and cruising in 5th at 70mph has it at around 42psi. So I think it is OK now that it is getting juice from a more reliable source.
I probably didn't need to RTV it, but I did it just to be sure. I put it at the very end, so 90% of the threads don't have RTV on it (by very end, I mean on the last thread or two that enter the adapter, not the first few that enter as you start screwing) just to create a seal around the outside. Hopefully it is OK. Hope TN is treating you very well Blair!

chris will this work with an aftermarket temp gauge? replacing the stock gauge..i want to do this to my cluster but i dont want to loose anything electrical....if there was a way you did it and still everything worked the way it should let me know thanks

You want to replace your stock temp gauge with an aftermarket one? Just do what I did with my boost gauge. Use a VDO Vision gauge and sender. LMK if you have any additional questions.

I did the same thing on my Miata.
http://picasaweb.google.com/cscarpulla/MiataGauges#

C

Second edit: Turns out, my original grounding locations may have been OK. After some other issues, I figured out that my engine to chassis grounds were in really bad shape. I had the VDO gauges reading incorrectly, the OEM temp gauge, and the car wasn't starting very well. After putting in 4 new engine to chassis ground wires using 6 gauge wire, all is well.

Edit: I found the problem with my gauges and will change this post to reflect the answer. I had been getting incorrect values on my gauges over the past little bit. This was exemplified on my last interstate trip. I have oil pressure and water temp gauges hooked up and an oil temp gauge which is waiting for spring to drop the oil pan. I drove 5 hours to my sis's house on the interstate and in 5th gear at 70mph, I was at about 240 degrees F water temp and 20psi of oil pressure. At a stop light, I was at 0psi of oil pressure and pegged at 250 degrees F water temp. After fiddling around with the grounds, I got them working correctly. Originally I had all three gauges individually grounded (a single 14 gauge wire from the gauge directly to an individual bolt). I used the 4 bolts under the panel under the steering wheel, two of which you can see below:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03920.jpg

To fix it, I grounded it to another location, similar to how JimR did in a previous post:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03922.jpg

That picture does not show the real end product, although I did ground the gauges to that spot. This is what I did. For my three gauges, there were a total of 6 grounds (3 for gauge lights, 3 for the gauges). For the lights, I wired the three light grounds in tandem with 14 gauge wire (similar to the pic below but that is the power wire).

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03923.jpg

Now I had 4 ground wires, one from the tandem light ground wire and 3 from the gauges. I merged two of the gauge grounds into one terminal, and did the same with the last remaining gauge ground and the light ground. To each of these I connected a 10-gauge ground which ended in a ring terminal which connect one of the two screws by the gear shifter as pictured above.

Now I am running a constant 40psi of oil pressure on the interstate and my coolant temp gauge sits around 185-195 on the interstate. At idle, I'm about 10psi of oil pressure. I'm much happier!

While I wait to see what happens with my new grounds, or if someone has an idea what could be wrong, I thought I would post up a bit more about my install.

When attaching the mounting plate to the dash, I followed Chriscar's lead and fabricated brackets using a bar of "L"-shaped aluminum (1/16" x 1/2" x 3/4"). At first I tried gluing the mounting plate to the brackets using Gorilla Glue super glue, but it was very flimsy. So I mounted it instead using these screws I found at Home Depot:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03915.jpg

I drilled the holes for it using a 1/8 drill bit. I had to enlarge the holes a bit in the aluminum to get the screws to thread, but the plastic mounting plate was giving enough to not need any further work. I just threaded 4 in halfway and it is holding on nicely. Here is a pic with one screw in, the other on the paper bag to see what it looks like:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03913.jpg

And both screws in:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03914.jpg

Next the lighting of the gauges. The bulbs that come with the VDO gauges are pretty weak IMO. So I bumped it up with these (VDO bulb on the left):

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03942.jpg

I got the cool white LEDs to match the bluish hues I now have in my cluster. Here are how the LEDs compare to the VDO bulb out of the gauges:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03930.jpg

New bulbs installed:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03940.jpg

And now a bad pic of the new look of the cluster and center console. I can see the gauges much better at night now!

http://i713.photobucket.com/albums/ww131/Clava_06/DSC03939.jpg

My issue all along appears to have been the engine to chassis grounds, not the gauge to chassis grounds! I adjusted post #64 to reflect both the issue and my solution.

Because the water temp gauge is so far from me and the sight-line angle from my driving position can be great enough to misread the gauge a bit, I wanted to find a solution which turns the faces of the gauges towards the driver's side. I tried and failed. I ordered an angle gauge panel off ebay:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=290530308954&viewitem=

It is a nice piece but it is too big to fit in the center panel and it wasn't going to fit too easily behind the center panel. If I get another center panel to mess with I might try it again, but for the moment I'm back to where I was. If anybody has any other ideas I would be happy for the help. Here are a few pics of the piece I got from ebay, in case it might suit you in a different application:

http://i713.photobucket.com/albums/ww131/Clava_06/DSC05370.jpg

http://i713.photobucket.com/albums/ww131/Clava_06/DSC05369.jpg

http://i713.photobucket.com/albums/ww131/Clava_06/DSC05373.jpg

for oil temp couldn't you use the vdo m10x1 sender and then just use a nut with jb weld?