Bringing old gauges back to life

[lt1kicker]

Need to know some hints or tricks here

79 Chevy Scottsdale w/ upgraded gauge package featuring voltage, temp, oil pressure, fuel, speedo/odo.  Problem I have is that not a single gauge works.  The only guage I can get to do ANYTHING is the temp gauge seems to act like a voltage gauge, meaning it pulses w/ the turn signal, headlights, brakelights, sort of like an overstrained voltage gauge.  The speedo must have stopped long ago, as the truck was advertised w/ 180k on it and it shows 164k on it.  There is also NO backlighting whatsoever on any instruments other than the wiper switch. 

What do I need to start checking for?  Are each individual sensor bad or could this be one big electrical problem? 

[Blazin]

Sounds to me like someone put the wrong year gauge cluster in it. Could be other problems but the pulsing temp gauge reminds me of when years back I tried putting a 76 gauge cluster in and 84 truck. Spedo could be the spedo, cable, or the gear reduction thing a ma jig on the transfer case.

[lt1kicker]

Well, I discovered that the fuel gauge works as long as the headlights aren't on.  If I turn the headlights on, the fuel gauge quits.  Sounds to me like there is a ground that's gone bad.  What is the location of the common ground(s)?

[Blazin]

There are several grounds on the parking brake bracket. Plus a few under the hood for lights & motor to frame and body. should be one from bed to frame, & one behind right tail light assembly.

[lt1kicker]

Ok.  I'll check that location tonight.  I was able to snip the ground to the fan blower motor and make the heater stop!  It was a tad bit warm, ALL THE TIME.  I'll install a switch or fuse to that and turn it on in cold weather. 

[Blazin]

You could have just unplugged it under the hood!

[lt1kicker]

Ordinarily yes, but it looks like someone has been doing some homestyle wiring under there

I'm wondering, since I know my fuel gauge works, but my speedo is completely dead, what to check for on the speedometer.  Is this a common easy fix? 

[lt1kicker]

Pulled the cluster tonight.  Not as bad a shape as it looked.  Most of the bulbs do not appear to be "blown" so I'm wondering why there is no power getting to them.  Could this be a bad headlight/dimmer switch?

[75 C20]

I'm wondering, since I know my fuel gauge works, but my speedo is completely dead, what to check for on the speedometer.  Is this a common easy fix? 

just an idea but when i put my speedo cable back on my 75 i thoguht i had put it on good then when i took it out it wouldnt read so i took it off at the tranny and made sure the cable went in the hole into the tranny not slip off to the side like mine was-
u could take it off at the tranny and put it on a drill and have some one c if it show ne thing

[lt1kicker]

Yeah, I'm going to check that cable.  I guess it goes into the transfer case on A 4X4?

[79GMCSC]

I'm just wondering what the number is on the printed circuit? It usually starts or ends with PED, if you want I can tell you what the application is for that particular circuit.

[lt1kicker]

Not sure where to find this #

Would it be on the back of the cluster?

[79GMCSC]

It would be on the printed circuit itself. You would have to pull the gauge cluster out and look at the back side of it. The number usually runs vertical on the circuit and like I said before there is usually a PED written before or after the number. Hope this helps.

[lt1kicker]

Ok.  I'll look in the morning.

[lt1kicker]

Well, I pulled everything and put it all back in.  I wrote down the PED number but don't know what I did with the paper!

Anyway, it has to come back out.  I've got nothing.  If I use the headlights or turn signals the fuel gauge quits working.  AFAIK the oil pressure gauge seems to function, it displays pressure at least.  I've got nothing out of any other gauges.  I also only have a fasten belt light, nothing else.  And I seem to ahve lost my hi-beam lamp, which did work.  Also don't have turn signal indicators that work.  So, What gives?  Do I need to just replace the whole cluster?  Backlighting does not work either.