Instrument cluster on my 72 C3 is dead. Where do I start? Fuse box?

 

What do you mean by dead? Speedo and Tach are both cable drive. Are you talking about the center stack?
The first step of any diag is start with fuses.

 

Clock is a separate fuse from other gauges. Oil press on early cars is mechanical. Amp meter is wired differently than other gauges.
What is dead?
EVERYTHING?
I would then think, ground. (On A piller behind the drivers dash).

 

Is it just the lighting that’s out? Agree with 4-vettes… ground or lack of ground is a common thing that can cause many issues on these glass cars. If you do pull that cluster, I recommend running an additional ground as well. You don’t want to revisit the cluster removal process again if you can avoid it.

 

There is a ground with a double wire female terminal that hooks to a male terminal stud down near the cigarette lighter. Without that you would have what you are experiencing.

Bill

 

The speedo and tack work............. none of the center stack works. While I'm in there, thinking I should replace all the bulbs as well???? Anything else I should look at before closing it back up??? Anything I should be careful of as I take center stack apart?

Appreciate everyone's expertise sharing and knowledge..

 

The car is over 50 years old. You should be extremely careful with absolutely everything. You should check , clean and check again absolutely everything. Every contact, every wire, every everything.
And remember just how old and brittle everything is. Be careful, and be extremely thorough. You don't want to keep pulling it apart over and over. Just increases the chances of breakage.

 

Welcome to the Corvette Forum Seventy2! This is the place to be when you have issues or questions regarding your Corvette!! We are glad you have joined us and look forward to helping you in any way we can!

First, I would take a look at the Fusible Links used in the C3's. I have a 1968 C3 and my fusible links are located down by the starter motor and they go upwards towards the alternator and connect to my Horn relay which in turn activates the fuse block bringing power back into the entire car.

While not being sure where they fusible links are located on a 1972 Corvette I will guess that they might be where the ones on my C3 are. These 2 fusible links were installed to provide your Corvette a "Last Chance" at survival during a bad electrical short. If the car has experienced a really bad short then it is possible it might have burnt the two fusible links. Frequently the owner would remember the short after one extreme enough to burn both fusible links out. My car was using a Electric cooling fan controller and one day the controller decided it was time to burn up and started emitting smoke while going through the start up. The short was indeed bad enough to take out both fusible links saving my car's electrical system. Fusible links are available on Amazon or better yet your local NAPA store should have them as well. You need to replace each one with the same size link that was in the system before. They also need to be solder into the electrical system and covered in a good heat shrink tubing. On my C3 the fusible links look like tubes made of rubber over the wire. You can check their continuity by using tiny needles pushed through the wires but I prefer a multi-meter. Any time you make a hole in a wires insulation you should try and plug it up or cover it up to keep anything from getting inside the wire's jacket and causing corrosion which leads to high resistance and more problems.

In a rough sense the power comes out of the alternator and get sent to the battery. The fusible links send power from the starter up to the fuse block and from there the power is distributed all over the car. First check your battery and record the voltage. Then check your Horn relay and see what the voltage is there. If there is no voltage at the horn relay then this might explain why your fuse box is also acting up. If the voltage is making it to the fuse box measure it as it should be close to what you saw on the horn relay.

Grounds on a Corvette are an "ongoing issue" so if the fuse box IS getting power then I would start looking at the dashboard ground connections. Battery Connections should be cleaned every year or two, this means checking the ground cable connection at the frame and removing the parts, cleaning the surfaces and then reassemble. I like to use Battery GREASE and cover the ground cable junction to keep air from getting into the connection and causing issues.

 

I would replace the oil pressure gauge feed line while you’ve got the center gauge cluster out.
Many people have posted problems with the quality and fitment of new replacement bulbs, so do your research as to which ones have the best fitment.
Be extremely careful removing and replacing anything.

 

Replacing the oil pressure line that goes to the center console oil pressure gauge is a wise move!
Personally, I have had enough hot oil sprayed on my flesh while driving fast for a lifetime. I put the -3AN Hose kit that replaces the nylon line used in the pressuyre gauge connections. The other choices are the soft copper, a replacement Nylon tube or the AN Line which is the toughest of the group. They sell the various kits with the adapters needed to make them work in your vehicle.

While your dashboard and center console are apart be sure to clean the light sockets and power connections with either #2 Pencil's Eraser or some DeOxIt which is a liquid chemical cleaner. The DeOxIt will clean decades of corrosion in a swipe of the rag. Use it liberally on the electrical connections and the fuse box itself and your electrical system will appreciate the help.

Double check the Grounds for the dashboard area before closing the dashboard up again.