Mayt13

Hey Guys,

I originally posted this to Tech/Electronics but no one has responded and Im returning to semester soon, so I need to get this done!

only the tachometer is working and the oil pressure gauge intermittently. My coolant temperature is dramatically bouncing as though it has a poor connection. Fuel reads full all the time. Even my speedo (although this is a mechanical connection IIRC) is completely not functioning.

I have checked (with a test light) all my fuses and they seem fine. I reconnected the speedo cable after I recently dropped the transmission (to solve an unrelated issue). I didn't see anything too complicated (just a square tipped wire fitting into a square hole).

I thought maybe I had forgotten to reconnect the gauge cluster power wire to the starts positive node, when I went under to check, everything seemed fine.

Im having trouble locating wires/sensors. Looking at a wiring diagram is fine and dandy, but How do you find the actual routing in the car, or the sensors mount points?

Also how do you trouble shoot with a multimeter, I only partially get it.

Mayt13

I'm still stumped guys if anyone wants to pitch in their five cents...

Scorpner

iTrader: (4)

The amount of questions is a bit daunting (6?) and I know that I've posted the answers to a few of them a few times already. A search (both on here and google) may provide a lot of the answers for you as well. Make sure you're using a GM manual and not Haynes etc. as they can leave you guessing.

Below are the locations of the temp an oil sending units. There is a description of testing the gauges on here and what I recall is grounding and then applying voltage to the wire going to the sending unit. IIRC the voltage should be 5v as that's what I recall the sensors working on.
Listed as "80" below is both locations for the oil sending unit/s. The location depends on model. The temp sensor is located at “76” on the diagram:


Here is one of the threads i posted in: https://www.thirdgen.org/forums/elec...gauge-not.html
Another: https://www.thirdgen.org/forums/elec...ster-woes.html

There should be some info for you to take from that and read what others have posted as well. They often know more than I do.
When you have multiple electronic issues the first thing I look for are faulty grounds. Voltages tend to float when circuits are not grounded properly which can cause multiple issues.

A multimeter is a great idea, I recommend buying an auto ranging multimeter that can read amps. There are many techniques from reading voltages (pressure), resistance (restriction), continuity (no restriction (actually very low)) and amp (flow rate).

• Reading resistance (Ohms) can be tricky if it's done on an assembled circuit board as associated components can affect the reading. Resistance is always conducted with the power off as the meter supplies power for that function. If the manual states to test resistance a certain way then you should be able to trust that is the correct way of doing it.
  .
• A derivative of resistance is a continuity checker with a beeper. This is handy for checking grounds by attaching one lead to the chassis (or other ground) and then say the ground on the cluster circuit board, or alternatively to the fuse block if you want to check a power circuit. It all depends on what you want to check. If there is no connection than that's called an open and the beeper won't go off. If the connection is there then it will beep. It's a faster way of checking opens and shorts and saves time troubleshooting. A short may be where a wire wears through and touches a ground like the chassis or other metal part. Then in this case when it beeps it means that it is shorted to ground and the flow of electricity doesn't make it to it's destination. If you have a partially open ground then you would need to go back to reading resistance and most of the time compare it to a written document like a manual or compare it to a functioning car that is the same. (This can also be tested with a volt meter as described below.) Partial ground can cause the voltage to fluctuate and/or offset the circuit causing multiple failures.
  .
• Voltage checks can be used to test the charging system, battery capacity, proper circuit function as well as open and shorts. Voltage tests are done with the power on. A common analogy in electronics is to compare electricity to flowing water where amps are the rate of flow, voltage is pressure, and resistance is a restriction. So if you have resistance in a circuit, pressure is going to build up on one side and that difference in pressure is the voltage. So instead of using the ohm meter, with a live circuit you use the volt meter to check the voltage difference on each side of the resistor. But as stated, other parts of the circuitry may affect the actual reading and that's where documentation or comparison comes into play.
  Real world uses include monitoring the voltage drop while turning the car over (indirect cranking capacity). Voltage reading with the car off (battery stability), and also while running (alternator).
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• Using the amp meter is good for finding slow drains on the system which can kill a battery when the car sits for a period of time.

Your gauges work as a kind of volt meter itself with the sending units acting as variable resistor. So as say the temp value or oil pressure changes, so does the resistance, and that affects the needle on your gauge. Many GM circuits depend on ground to complete circuits which allows use of a single wire vs. two in more typical situations. Also note that you need the correct sending unit for your gauges or they may not work correctly.

Disconnect and try turning your speedo cable at the cluster end with the transmission hooked up. It should not move, If you're quick you can spin the speedo unit on the cluster and get it to move slightly. If you happen to have both ends of the speedo cable free then check to see how freely it turns. Sometimes they need a little grease from what I recall.

Mayt13

Thank you so much, I will read though all of this carefully. I did do both the Google/ThirdGen search. Perhaps I did not use the right keywords since I didn't find much...

Regardless, I will have to pick up a factory manual. I have one for my motorcycle and it's been extremely helpful. Thanks for the info!

Scorpner

iTrader: (4)

Glad to help!
Sorry for assuming you didn't do a search. I guess I can see that as I know Google hasn't been as useful as it used to be, and yes specific terms seem to matter more than it used to.


Helmsinc.com is the best source and I picked up mine when they had a big sale going on. They are expensive otherwise.
Also, CL, or Ebay is sometimes a good place to find them. I even found a Corvette set in a used book store. lol

gmkid

I agree with scorpner start by chasing down the circuit grounds on the cluster wiring. Your fuel gauge reading full is a telltale sign of a lost ground. A fuel gauge is just a voltmeter with the numbers replaced with F 1/2 E. The float in the tank is a float device hooked directly to a variable resistor (potentiometer) changing the voltage to the gauge. This is a good place to start and may fix other issues. Get a good GM manual and check for continuity "beep out" the wiring. Good learning project.

Joe Tag

iTrader: (4)

These are just guesses at what your problem is, we have limited information. I know you said you checked the fuses with a meter, but pull the gauge fuse and make sure it isn't corroded and getting intermittent contact. I am taking a shot at it being a Camaro since we don't even know that. This is one diagram I have searched endlessly for, no luck. I have found the 91 92 cluster pinout only. Pin 3 & 8 on the left and pin 2 & 7 on the right are the grounds to the cluster for those years. If it wasn't such a PITA to pull my cluster I'd go out with a meter and check it. You can try and see if the same pins are grounds on your earlier model. If they are grounds and are good I would look at the place they contact on the cluster and see if they are corroded. Clean them up with a pencil eraser or some vinegar.