Problematic Fuel Gauge Wiring

[sixpointsixliter]

Hello! My name is Carl, I've just joined and have been browsing the forums for awhile and am really enjoying the atmosphere. I'm not exactly sure weather or not I'm posting this in the correct location, but using common sense I think it fits.

I have a 1977 GMC Jimmy high sierra 6.6L I've torn out all the electrical in it and am in the process of redoing it. The stock Fuel Gauge has three terminals in it which connect (using some crazy metal backets) to the circuitry on the instrument panel. Well...you see...I have removed that and I've now stuck myself in the classic "which goes where" situation.

I've just installed a new gas tank/sending unit/ straps, and have made a new ground and ran a new signal wire all the way to the gauge up front. I believe it requires a 12volt+ a chassis ground and signal wire to the sending unit, but have no idea which way, and don't want to get it wrong for fear of sticking 12v to a grounded gas tank with 31 gallons in it...

Any help would be greatly appreciated, Google and my Haynes/GMC maintaince books haven't given me exactly what I was looking for.





Video is about 6 years old but...
https://youtu.be/lwBwetg2Uzo

[87Skier]

Welcome to the forum! I see that you posted in the 69-72 Blazer section, but you have a 77. It's usually best to post in the 73-87 section, or one of the subsections covering the 73-91 Blazers and Suburbans.

Anyways...

I happened to have a gauge cluster that is identical to yours.
Looking from the back of the gauge:

Left post - Fuel signal
Right post - 12v signal power
Bottom - ground

You can trace the circuit board and should be able to see that the left post does not go to any lights. It goes from the gauge directly to the connector.

Alternatively, you can test this setup by supplying 12 volts to the right post and grounding the bottom. The gauge should go to about 3 o'clock (way passed the full mark). Shorting the left post to ground will cause it to go to completely empty.

[sixpointsixliter]

Originally Posted by 87Skier

Welcome to the forum! I see that you posted in the 69-72 Blazer section, but you have a 77. It's usually best to post in the 73-87 section, or one of the subsections covering the 73-91 Blazers and Suburbans.

Anyways...

I happened to have a gauge cluster that is identical to yours.
Looking from the back of the gauge:

Left post - Fuel signal
Right post - 12v signal power
Bottom - ground

You can trace the circuit board and should be able to see that the left post does not go to any lights. It goes from the gauge directly to the connector.

Alternatively, you can test this setup by supplying 12 volts to the right post and grounding the bottom. The gauge should go to about 3 o'clock (way passed the full mark). Shorting the left post to ground will cause it to go to completely empty.

You are a life saver! Thank you for the welcome, I apologize to you and anyone else, On the fourm home it has a 69-72 Blazer section and a 73 - 87 pickup section. I must have missed the 73 - 87 Blazer/Jimmy sub. Sorry for any inconvenience.

[87Skier]

It happens all the time...