Author Topic: Guages not working  (Read 161 times)

Offline MY1978

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Guages not working
« on: November 22, 2020, 10:31:41 AM »
Hello -

Refurbing interior and dash of my 1978 Chevy C10.  My original gauges were not very pretty anymore.  Saw that I could get overlays, but concerned about them peeling away with time and heat/cold.  Was at my now favorite bone yard and came across a pristine set of gauges.  I know you are always taking a chance, but they LOOKED so good!!!!  and so brought them home.  I installed them into the cluster backing after replacing the printed circuit panel and cleaning up the clips.  When I start and warm up my truck, they do not register.   :(     All instrument cluster lights work as well as cab/cargo lights.  They just are not registering.  I know there is a possible/probable problem with fuel sending unit so not concerned about that quiet yet.  Please help.  Pics attached showing original cluster with needle positions as well as fast, mid and low idle pics for newish gauges.  I am sure I am going to be told to buy new gauges, but is there anyway to test these first?  I am unfamiliar with proper way to test so please explain in laymans terms.  I know what a multi meter is and have a small one I can use.

Thanks

Offline bd

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Re: Guages not working
« Reply #1 on: November 22, 2020, 01:18:43 PM »
Check and replace the 4-amp "CLUSTER FEED" fuse and burnish the fuse socket contacts.  Make sure that the replacement printed circuit board matches the original and that no circuit foils are shorted together around the margins of holes that are specifically punched to sever the foils.  For a description of gauge function and testing see the technical article Functional Tests of Factory GM Electric Gauges.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline MY1978

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Re: Guages not working
« Reply #2 on: November 24, 2020, 01:33:20 AM »
Okay, thank you.  I have verified that the printed circuit panel is installed correctly and that nothing looks shorted together at openings or clips.  I followed the old circuit panel when placing the clips.  When you say to make sure the replacement printed circuit board matches the original, you are speaking about the path of the foils - correct?  How would I do this?  Hold both panels up to light to see if any difference? 

I will be replacing the 4amp fuse today - had to get a fuse puller.  I plan on replacing all the fuses as I am more than certain that some of these or 40+ years old and as you can see from the picture, some areas need to cleaning/rust removal.

Thanks for your help with this. 
« Last Edit: November 24, 2020, 10:47:51 AM by MY1978 »

Offline bd

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Re: Guages not working
« Reply #3 on: November 24, 2020, 11:05:12 AM »
The AGC/SFE fuse panels are prone to oxidation of the fuse end caps and their sockets because of the metallurgy employed and the fact that the fuse connections are not physically shrouded, thus, readily exposed to dust accumulation and moisture.  The 4-amp "CLUSTER FEED" fuse supplies ignition power (I+) to the gauges.  Cluster illumination is powered via a separate fuse supplied by the headlamp switch and battery (B+).  Cleaning the fuse panel sockets can be tedious and requires patients for success.  When oxidation is particularly heavy, a Q-tip bearing some fine-grit valve lapping compound followed by rinsing with alcohol to remove all of the residues will suitably burnish and clean the fuse sockets.  A sparing application of silicone dielectric grease following cleanup of the fuse sockets will retard subsequent oxidation.

Another common source of cluster electrical trouble is the instrument panel harness-to-cluster connector.  Again, oxidation gradually interrupts continuity between the 18-pin harness connector and the printed circuit board (PCB).  And, don't neglect the dash ground connections to the park brake pedal frame attached to the left kick panel.

Regarding the PCB, if GM part numbers are printed on both PCBs, compare them.  If not, trace the circuit foils carefully to make sure they are exact duplicates of one another and running to the same places.

EDIT:  Looks like the 4-way hazard flasher is missing, too.
« Last Edit: November 24, 2020, 11:08:17 AM by bd »
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline MY1978

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Re: Guages not working
« Reply #4 on: November 24, 2020, 12:26:50 PM »
Okay, thank you for all your help.  I popped the 4 amp fuse, sprayed with electrical contact cleaner, used a folded piece of sand paper, sprayed again with contact cleaner, put dielectric grease on cleaned contacts, inserted fuse and VOILA'  I have gauges again.  Thank you so much for walking me through this.  Moving on to cleaning all the other contacts and replacing the fuses.  All the fuses seem to be AGC.  I assume I have to stick with AGC's.

Yes, I have the 4-way off out of the way for fuse pulling.  Thanks for noticing though.  :)
« Last Edit: November 24, 2020, 12:42:56 PM by MY1978 »