Are 1981 and 1977 Insterment Cluster Wiring the Same as My 1979

[AJ 3]

Are 1981 and 1977 Instrument Cluster Wiring the Same as My 1979 truck.

I found a 1977 and 1981 Instrument Cluster and swapped speedometer, fuel gauge, and lighting to build a factory looking cluster with idiot lights. To replace the HACKED "custom" aftermarket not working cheep gauges installed by a PO on my 1979 truck.

Without the Instrument Cluster plugged in all of my exterior lighting and everything else works correctly.

With the cluster plugged in my fuel gauge reads 3/4 tank and the internal and external turn signal lights work correctly.

Everything goes weird when I turn my headlights on. The fuel gauge now reads empty and my gauge lights are very dim and don't change when I turn the headlight knob. My interior turn signal lights also come on and dim when I twist the headlight knob. The interior turn signal lights also now flash opposite of my exterior lights. Also my bright head light blue indicator light is on when my low beam head lights are on but goes out when I switch to brights.

Do I have to search for a working 1979 instrument cluster to solve my issues or do I have something else wrong with my 1979 truck.

 

[bucket]

So what year cluster and printed circuit are you using? '77 will not work without re-pinning (that year has mechanical oil pressure), but the '81 model should work fine in a '79 truck.

 

[Green79Scottsdale]

Yeah, what bucket said! ^^^^

My first thought too was that your printed circuit and wiring didn't match up. I am not sure if the printed circuits and sensors are different for idiot lights compared to gauges either. An electrical diagram should help in figuring out what wires need to be re-pinned and where for idiot lights and the printed circuit you are using.

 

[bucket]

Yeah, what bucket said! ^^^^

My first thought too was that your printed circuit and wiring didn't match up. I am not sure if the printed circuits and sensors are different for idiot lights compared to gauges either. An electrical diagram should help in figuring out what wires need to be re-pinned and where for idiot lights and the printed circuit you are using.

Oh good point! His '79 may have been an idiot light cluster before the gauges were hacked in, and that will cause problems because the pinouts are different.

I always forget gauges weren't standard. I've only had one with idiot lights, and I haven't even driven that one.

 

[AJ 3]

Currently I am using the blue holding fixture from the 81 with the speedometer and fuel gauge from the 77. I also have installed the printed circuit from the 81.

The 77 cluster had factory gauges that are not installed
The 81 cluster had factory idiot lights that are not installed

I believe that my 79 cluster had idiot lights when the factory 6 cylinder was installed. I wanted to keep the factory idiot lights but the PO cut the factory sending unit wires when the 350 was installed.

So currently just the factory speedometer and fuel gauge are installed along with all the back lighting bulbs and turn signal bulbs. Non of the other gauges or idiot lights are installed or hooked up. My main goal today was to make sure all the systems are working correctly before I install my after market gauges.

Since all my issues started when I turn on the headlights could a bad headlight switch cause the issues or do I have more problems.

 

[chengny]

It looks like the pin outs are very similar betweeen the 79 and the 81 (I only had the diagram for an 83 - should be okay to use). It will just take some time to determine which leads are not leading into the plug correctly. The 1979 dwg even comes with a key that indicates the function of each color/mil wire - and of course the pin location.

1979:

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1983:

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Eric Cartman:

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[chengny]

Everything goes weird when I turn my headlights on. The fuel gauge now reads empty and my gauge lights are very dim and don't change when I turn the headlight knob. My interior turn signal lights also come on and dim when I twist the headlight knob. The interior turn signal lights also now flash opposite of my exterior lights. Also my bright head light blue indicator light is on when my low beam head lights are on but goes out when I switch to brights.

All it would take is for one section of the rheostat controlled illumination circuit (pin 8 gray wire) to be making contact with the common ground circiut - the dimmer would then back feed all the lamps. That would equalize the voltage across the ones that were supposed to light up (causing them to dim or go out) and also make the lamps that were supposed to be off - light up. The panel back lighting would be basically disabled and the highbeam, directionals, seatbelt, etc. will brighten or - as in the case of the blinkers - cause the flasher to malfunction. The gauges themselves would also peg one way or the other.

 

[AJ 3]

After sleeping on the issue I feel that I might have a ground issue due to fact that my interior turn signal lights flash opposite the outside lights when the headlights are on. I also agree with chengny that everything is back feeding through the headlight switch. Now the issue is finding the problem.

Thanks for the wiring diagrams I will print them out today and trace the wires after work to make sure everything is correct. The diagrams in the back of my Haynes manual are very much lacking.

I did trace the circuit on the back of both the 77 and 81 gauge cluster and they seem to be identical with the exception of gauges vs idiot lights. So everything should work as planned once I find my electrical issue.

Thanks I will keep everyone posted

 

[AJ 3]

Yep it was disconnect ground wire. Everything was back feeding through the headlight switch. I honestly think the the ground wire has been disconnected for a very long time.

Now when I turn the ignition on a fasten seat belt light comes on. Plus I now have this neat light under the dash board that turns on when I rotate my head light switch.

For the first time since I have owned the 1979 truck (3 months now) everything electrical works.

Just 1 simple ground wire that totally confused the crap out of me.

Thanks very much for everyones help.