Intellitronix Gauge Installation in a 1976 Corvette
Here is the breakdown of the directions that I made for installation of the Intellitronix gauges. This was based on the 1975 electrical schematic and the directions directly from intellitronix and over the phone. I don't know if you have their directions, so I'll summarize.
First: Disconnect battery.
Second: Remove all gauges and bezels. You will need to customize the bezels somewhat to get them to seat properly. I removed it all and brought it inside to my workbench.
Third:
1. Sending units.
a. Temperature senders- you need two of the ones from intellitronix. They come with the kit. The gauges include a coolant temperature and an oil temperature. It does not have a clock. These are easy replacements if you can get the old one out. I am putting the second one on my intake.
b. Speedometer sender- If you have a cable driven speedo like mine, replace the sender with one of theirs. It converts the rotation into electrical impulse. ? What to do with the cable. I am removing mine, since I do not plan to return it to stock.
c. Run temperature safe wire through the firewall to these senders.
2. Bezel mounting
a. The smoke gray plexiglass that they give you almost perfectly fits directly over the gauges. It doesn't replace the plastic bezel lenses that are already there. You may have to file an edge or two down to fit. I drilled a couple of holes to match holes in the bezels and attached the plexiglass with small bolts. Remember to use the gaskets that came with the gauges originally. Get the board mounted the same way, using small bolts. You can get away with three bolts on each of the speedo and tach. 4 for the center cluster.
b. After the bezels are back together with the circuit boards, go and label the following wires and prep them for joining. I crimp fastened mine, but you can do it however you want.
3. Wire connections
a. All black wires go to ground. You can use any ground. I used a similar ground, the one from the original tach connector.
b. All red wires go to ignition on power. I used the tach ignition power wire (pink)
c. The purple one. This one was tough to figure out. The directions say to connect it to the parking light circuit, not the panel light circuit. After looking at the circuit board, it appears to be the wire for dimming. Therefore, I connected it to one of the gray wires which was used to light up the original speedometer bezel. This wire originally had a bulb on the end and grounded by mounting the bulb in the rear of the cluster. Since we don't need these bulbs any more, I removed them all and used one for each of the purple wires. The rest I insulated and hid behind the dash.
d. Speedometer-
1. White wires- connect both to a momentary switch. I mounted a small pushbutton that is located under the driver dash next to the bulb. This is how you calibrate the speedometer and how you can get 0-60 mph and 1/4 mile times.
2. The gray wire goes to the sending unit you mounted.
3. The yellow wire goes to the left turn signal wire (the light blue wire in the car) It is the only light blue one that came detached from the left of the speedometer.
4. The brown wire goes to the ebrake. This is the tan wire, circuit #33 in the diagrams.
e. Tachometer
1. The green wire goes to the original tach wire which is brown.
2. The orange wire goes to the right turn signal wire in the car which is dark blue.
The only dark blue one that came out from the back of the tach.
3. The blue wire is the high beam wire which goes to the light green wire which was attached to the back of the tach. (circuit 11)
f. Center cluster
1. Blue wire is the coolant temp wire. Connect this to the new temperature sending unit.
2. White wire is the oil temp wire. Connect to the sender you replaced with theirs.
3. Orange is the oil pressure wire. This directly connects to the original oil wire which is dark blue.
4. Yellow wire is the fuel tank sender. It connects to the tan wire (circuit 30) which is the original tank sender.
NOTES:
1. As you are disconnecting everything, take photos and label each cluster of wires as you disconnect them. It is very tough with the speedo and tach as they tend to all come out at once, but try. I did not take photos which made it much more difficult, but I did label everything with masking tape labels.
2. Take your time. Just identifying the correct wires took me a couple of days. If the directions were better, it would have been much easier.
3. These instructions worked for me and my car which is a 76. I do not guarantee that yours will be the same. Check with your electrical diagram specifically for your car if the wires are not the same.
Good luck, I hope that this helps and gets you through the project quicker than it took me. I hope that you enjoy the digital gauges as much as I do. Mike

Here is what I wrote up. I don't think from the directions written by RedBarron76 that he has the mylar printed circuit. Also, don't know if a 78 has it but I believe it must because the gage kit was for 78-82. If you have any questions, just e-mail me.
Nordskog Digital Gage Instructions
for 1978-1982 Vette
(My Version)
1. Disconnect Battery
2. For ease of installation, remove both seats
3. Remove side panels on console
4. Loose console and move backwards
5. Disconnect instrument cluster from console
6. Remove instrument cluster from dash
7. Remove all gages and printed circuit (mylar)
8. Remove and discard all existing lights.
A. Red wire on printed circuit goes to 12+Volts. I wired into fuse panel so is only on when ignition is on.
B. Black wire on printed circuit goes to ground (I grounded to alternator
C. Blue wire on printed circuit goes to new water temperature sensor located between Nos. 1 & 3 on left head. I had to use a bushing as I have the Vortec heads and it is a different size hole in the head.
D. Yellow wire on printed circuit goes to the fuel sender. The pink wire on the original harness was the wire from the fuel sender so I just spliced into this wire
E. Orange wire on printed circuit goes to the oil pressure unit. The brown wire on the original harness was the wire from the oil pressure sender so I just spliced into this wire.
F. White wire on printed circuit goes to the oil temperature sender. I installed the oil temperature sender near the oil pressure sender. Installed a brass tee into the block. Mounted the pressure sensor in same location as stock and mounted the temperature sender to the left if facing the left side of the block.
G. Purple wire on printed circuit goes to the dimmer circuit [instructions say the parking light circuit]. I spliced into the brown wire at the light switch.
H. You will loose any of the idiot lights that were in the original cluster.
9. Remove tach and speedometer cluster. A thru E are for the speedometer.
A. The two white wires on the printed circuit will have to be hooked to a momentary switch [not supplied, but can be purchased at Wal*Mart or Radio Shack. I mounted under dash in front of the steering Column. This is to set the speedometer for accuracy and also to check 1/4 miles, etc.
B. The red wire on printed circuit goes to 12+Volts. I spliced this wire into the hot wire coming from the instrument cluster.
C. The black wire on printed circuit goes to ground. I spliced into the ground wire on instrument cluster.
D. The purple wire on printed circuit goes to the dimmer [parking light circuit]. I spliced into the already existing wire mentioned above.
E. The gray wire on the printed circuit goes to the new speed sensor [white wire] on your transmission. You have to purchase this item extra. It does not come in the kit. You have to remove the speedometer cable, then attach the fitting that came with the sensor onto you transmission {where the cable did attach] and then mount the speed sensor. The black wire on the sensor must be grounded. I grounded mine on the transmission mount.
F. The red wire on printed circuit board goes to 12+Volts. Here again I spliced into the wire from the instrument cluster.
G. The black wire on printed circuit board goes to ground.
I spliced into the ground wire on instrument cluster.
H . The purple wire on printed circuit board goes to the dimmer [parking light circuit]. Here again, I spliced into the wire mentioned above.
I. The green wire on the printed circuit board goes to the tach. I spliced into the white wire on the original wiring harness which went to the printed circuit [mylar].
J. You have to reinstall the printed circuit [mylar] onto the speedo-tach assembly in order to have the turn signal lamps, the bulb showing when your lights are on bright, and the emergency brake light. Just remove all the bulbs in the remaining lights and re-install the bulb sockets.
K. Now you can start re-assembly. Two pieces of tinted plexiglass are provided to darken everything so you only see the readouts. Now is a good time to give your original bezels a good cleaning.

Note: I removed the speedometer cable completely and then ran the wires from transmission and the wires going to the oil, ground and temp thru this grommet.
Also, on the speedometer, you can run the wires thru the opening where the original cable was. On the tach, I removed the metal clips where the original tach board plugged in, and ran two wires thru two of the three holes that were there.

After the assembly is completed, take it out and calibrate the speedometer as per instructions that came with the gages. As I wired in each gage, I would connect the battery to see if it was operational, if so, I would then proceed to the next gage. Of course, you can not check the speedometer until complete but you can see if the speedo lights up.

The instructions are not that bad from Nordskog but hopefully this will help someone locate the wires that need to be connected for the original gages.
These instructions are for a 1979, the instructions say for a 78-82 so I would believe that they would be similar.

Hope this is clear as mud!!!
Roy