I have a 1977 L82.
1) Fuel gage was reading 1/8 tank at all times (originally worked until I replaced the printed circut board).
2) read about the resistors on the back of gauges and moved dk blue to oil gauge//lt blue to volt meter// and then I have 2 orange or faded red resistors for the gas gauge and water temp.
3) after exchanging the blue to orange (red) my gas gauge now reads 1/2 full on a full tank.
4) no other gauge works.......the clock does work
5) I have a short somewhere that is pulling my battery down. Currently am connecting and disconnecting as needed.
6) brake lights are very weak.
7) the overhead courtesy light is lit at all times (currently disconnected)
8) I have replaced the oil pressure sender and the water temp sender.
9) I have a new 100 amp alternator it has been checked and works.
10) new Optima red top
11) I checked the battery last night and it was reading 11.42 volts
12) checked current on battery with leads attached to + post and loose terminal and read 11.42 volts.
13) I have not gone the pulling fuse route yet

ANY SUGGESTIONS????????????????????

 

Why did you replace the circuit board in the first place? Did all these problems begin when you replaced the circuit board? Start looking where the problem began.

I have never heard of this, can you post a link for this or explain what this is about? Thanks

If you find you need a schematic for your car you can get a good color one from Don Olson - vetsvette2002@yahoo.com

 

the 4 ceramic "insulator" looking doo dads are actually resistors and are color coded to the amperage(?) lt blue = 125 or 130 amps
dk blue= is less red is 80 amps I believe and green is 75
These must be replaced in the correct order.
I originally replaced the pc because nothing worked on my center gauge cluster except the fuel and clock.

 

this was ripped from L82-1977


Could be an incorrect resistor on the gauge or a bad connection at the gauge/resistor/flex circuit.

There's a resistor on the backside of the gauge connected to the gauge and flex circuit. It is a piece of white ceramic with a color. The color tells the resistance. It is part of the calibration. You might have the wrong one for the year.

Each gauge has a resistor. They are easy to mix up if you take the flex circuit off. You'll end up with some strange readings on all the gauges until you sort them out.

Here are my notes on resistors:


There are color coded calibration resistors associated with each gauge. The first time I took mine apart I didn't recognize them as resistors. They don't look like a traditional resistor. I thought they were just insulators. There are a lot of older vehicles out that and I bet people have mixed them up over the years. They are flat ceramic rectangles that connect between two posts. They are color coded for value. From what I've determined, here are the values:

Disclaimer: I have never found this documented anywhere. It is not in the electrical troubleshooting manual. The color codes are not in the assembly manual. This is by trial and error testing and comparing other known unmolested gauge clusters.

Colors / Measured Values:
Light Blue - 125 ohms
Green - 90 ohms
Dark Blue - 83 ohms
Red or Orange - 85 ohms

I have also seen Pink on the oil gauge and Yellow on the temperature gauge in an original 1980 Vette. I don't know the values.


Here's the results of changing or mixing up the resistors:

Volts - Less ohms = higher reading
Gas - Less ohms = lower reading
Temp - Less ohms = lower reading
Oil - Less ohms = higher reading

The Light Blue (125 ohm) is used on the Volt gauge. If you use something with less ohms, the voltage reads higher. With a Green (90 ohm) resistor, the reading jumps to 18 volts from a normal 13.5V.

Red (90 ohms) is used on the temperature gauge. If you lower the resistor to 40 ohms (test) the reading will lower 25 - 40 degrees.

Dark Blue (83 ohms) is used on the oil gauge. If you lower the resistance to 40 ohms (test) the reading will jump from the normal 30 to 60.

Green (85 ohms) is used on the 77 Gas Gauge. Green on a 77 causes the low fuel light to come on with slightly over 4 gallons in the tank and it will show Full with a full tanks of gas. Red (90 ohms) will cause the light to come on at 2 gallons but the gauge never quite reaches full. Red MIGHT be correct for later C3's that have the 24 gallon tank. I haven't verified this.2-1977

 

Cool thanks for the good info!

You may want to tackle your short problem first, save the guages for later. Go the fuse pulling route and see what happens.

 

Wow. Great thread. good info.

I seem to have intermittant voltage / current running through the car. (you know when top of the door burns the bottom of your forearm and you get shocked reaching from the shifter to the console?)

Glad I saw this as I am having issues in all the guages, horn's out, windshield wiper motor / windshield washer motor's out.

Any info like this tracing voltage is good stuff.