Gauges inop

[Lifted1]

I have a similar problem. Temp gauge is pegged at the hot side. i replaced the sender. i've checked the wire. ive cleaned the bus bar ground. I've removed and cleaned the cab to engine block ground strap. i've used a test light and confirmed gauge terminals are hot. I've disconnected the cluster plug in several times. its clean and making connection.  no corrosion. With a test light there are 2 pink wires on the plug in that are not hot. #18? far bottom right corner and #7. not sure if these should have power or not or what they are connected to. The gauge cluster has power at all gauge terminals though.

The volt meter, temp gauge, oil pressure gauge, and fuel gauge are all not working. Dash lights all work.

anyone have other suggestions for me to try?

maybe the gauges have all gone bad one by one?  how do you verify if the gauge is bad? can you test with a multimeter?

thanks

[bd]

Welcome to the Forum!

Please include Year, Make, Model etc.. when posting

Ignition feed wires into the cluster are pink with black tracer.  Provide the truck model information so we can offer year/model specific discussion.  In the meantime, the factory service and wiring manuals are available in the Technical Forum.

[Lifted1]

i apologize. i thought i had replied to the 74 temp gauge thread?!  mine hasnt worked since i bought the truck.

1983 GMC C1500. No tach. 5.7l

[bd]

Unplug the temperature sender wire and see what the gauge does.

[Lifted1]

when i disconnect the sensor/switch wire the guage remains pegged hot. 

im not sure what else to do except start replacing gauges?? do gauges typically go bad? the volt meter, temp gauge, gas guage, and oil temp sensor are stationary.  i can move the indicator by hand by they go right back to where they position with ignition on.

baffling 

[bd]

Unplug the dark green wire from the coolant temperature sender AND unplug the 18-pin harness connector from the back of the instrument cluster.  Connect your test light between the dark green temperature sender wire and the positive post of the battery.  Does the test light illuminate?

Where do the needles of the oil gauge, voltmeter and fuel gauge point?  Be specific for each gauge.

[Lifted1]

extended sensor to positive battery terminal after unplugging from back of circuit board. test light works.

[bd]

If you're using an LED test light, test results can be misleading.  LEDs draw such low current to illuminate (on the order of ±0.025 amp) that excessive circuit resistance may net be detected, yet the circuit won't function properly.  Better to use an incandescent test light that gently loads the circuit under these circumstances.



^^^ This isn't quite what I wanted.  I want to know whether the green wire is grounded.  Disconnect both ends from the sender and the cluster, then connect your test light between B+ and the green wire.  If the test light illuminates, the sensor wire is grounded somewhere, causing the gauge to pin hot.





You indicated that you verified 12 volts to the voltmeter and all of the gauges using your test light.  Retest the voltmeter in a new unit of time, but this time probe both sides of the voltmeter, alternately, without moving the test light ground clip.  What happens?

Disconnect the tan wire from the oil pressure gauge sender.  With the ignition switched ON, what does the oil gauge do?





Unplug the fuel tank sender and switch the ignition ON.  What does the fuel gauge do?  Now, ground the wire that runs back up to the fuel gauge.  Again, what does the fuel gauge do?

[Lifted1]

 ok thank you for these suggestions. I will try them all tomorrow in daylight.

I did disconnect the connector from the oil pressure sender on back of engine intake side next to distributor. it was very difficult to reach. i ended up snapping off a brittle vaccum?/breather line that came out of the top of valve cover. Im getting a replacment now. i also heard a faint hissing and realized i was putting pressure on the compressor lines! eeeeek

with the wire disconnected the gauge pegged out all the way to the right. i have since reconnected it. bad sensor??  how do you verify oil pressure? i did drain and replace the coolant as well as replace the thermostat when i resurrected this truck. it hadnt been started in 8 years.  since the gauges werent working i didnt want to risk overheating it so i put a new thermostat in it and drilled a small hole in the thermostat prior to installing.

i refilled the coolant and verified it was circulating before i started driving the truck. The truck is my daily driver. It does get hot enough at idle and with a/c on to want to boil out of radiator when i twist the cap off immediately after a long idle. the fan seems to be working fine though. maybe this is normal? there is also a large vent type line that comes out the top of the exhaust manifold. it does tend to smoke a tad and has kinda a burnt oil smell to it. its not real bad though.

I will do all the other suggested test tomorrow and follow up. Thank you "bd" very much for the help. i do appreciate it a lot. 

[bd]

Replace the oil pressure sender (image) and verify the replacement has "60" stamped into the 9/16" hex nut adjacent to the threaded fitting.  If you've been driving the truck and the engine hasn't been rattling/knocking, it's building oil pressure.  If you want to confirm oil pressure (a good idea), thread a mechanical test gauge into the port normally occupied by the sender when you remove it for replacement.

The truck employs a sealed and pressurized (15-20 PSI) cooling system that is designed to be virtually air free.  As coolant heats and expands it transfers past the radiator cap into the coolant recovery tank where it sits until drawn back into the radiator as the coolant cools and contracts.  Hence, the effect of coolant pushing out of the hot radiator when the cap is removed is a normal and expected occurrence.

The "vent" line on the top of the exhaust manifold maybe part of the plumbing for a thermostatic (heated) air cleaner.  Posting a pic would clarify that.

[Lifted1]

hi bd,

all the local auto part stores have the 0-60 psi oil pressure sender but none of them have a "60" stamped on the hex.  some had the part number. O Rileys was $22 and the rest varied up to Napa $56.  I passed on all of them as i figured you were specific about the 60 for a reason.  Do you know where i can order one like you described?

When i unplugged the fuel connector under the passenger side of truck the fuel gauge moved to beyond Full. how do i ground the 6 prong fuel connector plug? jumper wire from what wire/prong to frame?

when i probed the volt meter with the test light, without moving the ground alligator clip, it only lit up on the right side (facing gauge) the other 3 prongs did nothing.

thanks again

[Lifted1]

forgot to mention,

i unplugged the gauge connector and coolent temp sensor. then i clipped the alligator clip to B+. when i touched the female spade connector end of green temps sensor wire nothing happened.  The test light is not showing it grounded.

thanks bd!

[bd]

In the following discussion, before replacing any gauge, make absolutely certain that the gauge is making good connections with the PCB through the gauge spring clips.  Oxidation between the PCB and spring clips, as well as weak spring tension against the gauge pins and PCB, are common problems.

Oil Gauge:
Telling you to check for "60" stamped on the fitting was misleading, because the statement was incomplete without an explanation.  There are several senders that look identical, but have different pressure calibrations.  The number on the fitting (when present) needs to match the maximum pressure of the gauge.  So, a 60 PSI dash gauge requires a "60" sender; an 80 PSI gauge requires an "80" sender, and so on.  It appears that some offshore sourced senders shed the identifying stamp.  Try to locate an AC Delco D8032 or equivalent.

Fuel Gauge:
Ground the sender wire that leads back to the fuel gauge and switch the ignition ON; the gauge should read Empty.  Pick up a 47-ohm resistor (minimum 1/2 watt rating) and insert it between the gauge sender wire (sender disconnected) and a shiny bare ground.  With ignition ON the fuel gauge should indicate 1/2 tank or a gnat's eyelash more.  If all works as described, replace the fuel tank sending unit.

Voltmeter:
The voltmeter has only two circuit connections, B+ and ground.  One of the three gauge pins is shunted to another by a ceramic resistor attached across the back of the gauge - one of the two shunted pins is B+.  The third pin not connected to the resistor is B- (ground).  With the gauge installed in the cluster clip your test light to a verified B+ source and probe the B- voltmeter spring clip.  Once you have verified B+ and B- to the voltmeter, if the voltmeter isn't indicating 12 volts with ignition ON, replace it.

Temperature gauge:
If you have an ohmmeter, measure the resistance of the sending unit on the "cold" engine and post the reading along with the guesstimated engine temperature.  Recheck the gauge connections through the PCB to B+, ground and sender.  If all are verified to be good connections, replace the gauge.