I've installed both gauges (Oil Pressure and Oil Temperature along with about 8 others at the moment) and the installation is very easy provided you know what you are looking for.
I went with mechanical gauges since they are cheaper then the electric ones but the install is the same regardless of the type of gauge you choose to buy.
If you remove the battery you will see two set screws. If you have purchased an a gauge with a 1/8" NPT fitting for either an electric sender or capillary (for mechanical gauges) you can just screw it in here and you are all set to go. Auto meter gauges come with everything in the box to install it right here.
For my oil temperature gauge I drilled a hole in the oil pan when I did an oil change. I have a drill press at home so this was easy and I borrowed a 3/4" or 1/2" NPT (I can't remember which one) drill bit and tap from a friend who's a machinist. After drilling and tapping I installed the capillary and it's been fine every since. BE CAUTIOUS NOT TO KINK THE CAPILLARY, if you do the gauge will be useless. Mine is bend pretty tight because I run the capillary on the driver side of the car before hand, then discovered it was MUCH easier to drill through the firewall on the passenger side. So my capillary was running pretty short. Even with that tight bend the gauge still works. Although sometimes it reads nothing then "shoots" up to the true reading. First time install and I learned many things. . . So don't make my mistakes. Although if I bought and electric gauge it would have been 100 times easier but I'm on a budget so you get what you pay for.
Here is the water temperature gauge this capillary was MUCH easier to run, and required the purchase of an 1-1/4" auto meter hose adapter. When you get the hose adapter it will come with 3/4 hose attachments as well, those are to be cut off before installation. Everything else is included with the kit. Even if you have an electric sender you will still need to purchase the hose adapter. Also remember to install the hose adapter to the upper rad hose. I'm told that the coolant flows from the engine into the rad in this hose. If you have an electric gauge you must ground the hose adapter to the chassis or engine. Don't worry auto meter has a grounding lug on the hose adapter and includes some wire with crimped ends in the kit.
I also have a boost/vacuum gauge installed. Although it only reads vacuum it's great conversation starter at car shows and costs the same as a vacuum gauge. so why not. For the installation for this gauge I tapped this vacuum line.
The voltmeter is pretty self explanatory. The EGT gauge will require a visit to an exhaust shop to get the bung welded on. Otherwise it's just running wires and following the directions. I also have a transmission temperature gauge for my manual transmission. For the transmission temperature gauge I had my friend machine me a new drain/fill plug that is made to have the sensor thread though it. I looks like every other adapter out there. The only difference is now I can use a regular wrench to change my transmission oil as opposed to the Allan headed socket.
I'm just waiting on the pillar pod to install my last gauges. Fuel pressure, wide-band O2 and a shift light.
If anyone has any more question about the gauges just let me know.