I have been trying to finalize the engine swap and carb conversion on my 88 and ran into this dash issue. My dash was fully functional the last time I tested it before replacing the clutch master cylinder a couple weeks ago. Now the dash intermittently lights up (sometimes fully, often times not) and when it does light up, I get no information.

I messed with the wire harness below the master cylinder and Im afriad that might be the problem. The only other thing I did to the car was connect the main ground to the engine block...

I just ordered a fsm (long overdue) but I was hoping somebody might be able to get me pointed in a direction. Im pretty stumped and frustrated. any help is appreciated

 

Did you check for loose connectors or grounds under the dash?

 

Update: It turned out I had a couple of blown fuses and the dash started working.

I originally had been using the factory tach through my msd, sortly after that I my dash went out. I switched to an analog tach, replaced the fuses and all was well. I then hooked the factory tach and shortly there after, my dash went intermitent and dead in the same way. The difference this time Is I can't find any blown fuses.

Any ideas?

 

and now the fuel pump isn't working.

I used the fsm to pin test the cluster and I had the correct voltages and grounds

 

Assuming the cluster fuses are good....its still a very fragile little chunk of solid state circuitry....LCDs and 5 lbs of solder and boards...lots to go wrong.

You might have sent high-voltage thru the tach wire by connecting or touching the wrong terminal. Hard to say...these things can be flakey and sensitive. Thats why GM discontinued them. Too costly back then as well. A new cluster in 1990 cost around $5000. I paid $1500 for a used one out of a wreck.

I guess you have traced the G-104 ground bundle? Critical connection.Should be 4 or 5 wires on that bolt.

Fusable links all in good shape under the battery?

The harness section where those grounds all originate behind the left side cyl head has several harness splices that are known for coming apart. They are cheap splices that GM wrapped in black tape and sent out the door. After some yrs, the wire rots and starts to break in or at the splice. If you can still access (engine out or top end off) that area of the harness on the firewall between the brake booster and the distributer, inspect it all where all wires exit the trunk.

Next would be the bulkhead connector behind the battery. Look to see if thats been damaged. The bulkhead block on the firewall on the passenger side is just a pass-thru and not a connector. Most of the dash wiring will be by the battery on that side.

There is also the possibility that you're developing the very common digital dash fault, a broken ground on a plug thats soldered into the main board in the cluster. Thats the normal point of failure that knocks out the lighting, goes dark, Blue hi-beam lite comes on, both TS arrows on. Thats easy to repair if you;re skilled with a soldering gun and have a good eye to look at the crack in the boards circuit.