My 78 came with just lights got oil, temp and volts. I would like to add a 3 gauge set to the car but would also like to keep lights hooked up.
The oil if I remember right I can use a "T" to do it behind the carb, Temp is what I'm not sure about. Do I go manual or electric and where do I put sending unit to keep light working ( Back in the day it went into thermostate housing, I do have a blocked hole there I could use).

Where do you have your gauges mounted? I see the most used place is above the console.

Pics for any of this would be nice.

 

The factory setup for temp is in the head, and all heads have a threaded port to accept it, so you can simply pull the plug from the other head and install the new gauge in the pass. side head. It will be close to #6 cyl. on pass. side, and close to #2 on driver side. I like mechanical temp and oil myself. You can T the oil fitting, or you can also pick up pressure above the filter on driver's side. There are two plugs there that might be easier to get to for a oil pressure gauge. I believe the smaller plug is the pressure side.
As for location, under the dash on driver's side really cramps your knee room. When mine were inside I mounted them at the top of the console in front of the map tray. As you can see in this picture my Camaro has the little cubby hole under the radio in the end of the console, where the 3 gauge set fit nicely:

 

Thanks Val. I didn't realize about the plug in the head I will use it. I'll check on the plugs by the oil filter. I'm going to rebuild the carb so the one behind it will be easy to get to also. gauges will probably mount above map box, just not sure yet.

 

Older Chevy heads don't have the plugged port in the head, but your's should be new enough to have them. I know the newer 882 heads I took off my 327 had them, but original "camel hump" Chevy heads didn't have the ports. My new aluminum heads also have them, but smaller than factory holes. Factory are 1/2" NPT.

 

The ones on my old Malibu didn't but the motor in the camaro is early 90"s vortec and it does. When we took the car out on saturday, for the first time I got on it some, Boy what a dog! When we can I want to put in a 1st gen 350 with around 325hp, and what I learned from years past and my JEEP, gears gears gears.

 

Or you could do some upgrades to the '90 Vortec 350! With the right cam, and those gears it might surprise you what it will do.