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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: AZAvery78 on December 13, 2012, 08:32:50 pm

Title: Just bought a 78 C10 and the only gauge that works is the Speedo and fuel gauge
Post by: AZAvery78 on December 13, 2012, 08:32:50 pm

So I just bought a 78 C 10 knowing the gauges were messed up. The Speedo works but the odometer doesn't roll over. The fuel gauge stays at full the whole time when the truck is on but the other gauges don't work. Also the back lighting to the cluster doesn't work so at night the whole cluster is black. One blinked light does work though.  Any suggestions on what might be the problem before I jump to buying a whole new gauge cluster? Thanks

Title: Re: Just bought a 78 C10 and the only gauge that works is the Speedo and fuel gauge
Post by: Jason S on December 13, 2012, 09:25:13 pm

Welcome to the site.

First thing, ensure that the cluster that is in your truck is correct for your truck.

Apart from the warning lights (idiot lights), there have been several different gauges used in the 73-87 dash clusters including mechanically operated oil pressure, electrically operated oil pressure, ammeter, voltmeter, various mph speedometers. 

Depending upon the factory wiring, the gauges from one year model may or may not work in another year model.  Additionally, if the truck had a gauge cluster swapped into a warning light equipped truck it will require some wiring changes.

Title: Re: Just bought a 78 C10 and the only gauge that works is the Speedo and fuel gauge
Post by: bd on December 13, 2012, 09:29:49 pm

Welcome to the forum from California.

Keeping what Jason said in mind, start checking the basics.  Check fuses, bulbs, the instrument cluster ground connection to the cab sheetmetal on the driver's side, electrical connections between the wiring harness plug and the printed circuit on the back of the cluster - make sure the harness plug is seated into the cluster housing, check the electrical connections between the gauges, gauge sockets and the printed circuit, check the dash light dimmer control, etc.  There's a good chance you have burned bulbs and multiple connection problems.  Be careful cleaning the printed circuit, because the foil will peel from the flexible backing easily.  The odometer not working is a mechanical issue.

Title: Re: Just bought a 78 C10 and the only gauge that works is the Speedo and fuel gauge
Post by: blazing816 on December 14, 2012, 09:02:20 am

I know with my truck the engine was replaced and the PO didn't care about keeping an eye on the engine so they did not install any of the sensors or sending units (that doesnt really explain the fuel gauges). I just am stated you may want to make sure you have the sensor and sending units first and they are pluged in. I spent alot of time trying to clean back of my gauge cluster, new gauges, and what not else, and they realized that there was not sending/sensor units in the engine to send the data.

Just figure you may want to start looking for those first... my $.02.

Title: Re: Just bought a 78 C10 and the only gauge that works is the Speedo and fuel gauge
Post by: AZAvery78 on December 14, 2012, 12:10:22 pm

Thanks for all the input. I am no genius mechanic by any stretch, so I will check all of these things when I get the chance over the next few weeks and get back.