fuel gauge not working when lights turn on

[blazer74]

^ look for a black wire pushed back in the connector at the cluster


Sent from my iPhone using Tapatalk

[Boxchevrolet]

i still haven't found the issue, I've traced every ground and they are all in place and making good contact, any other ideas?

[roger97338]

While researching that very same problem with my 1985 I found this site.  Mine turned out to be a bad plastic circuit board on the back of the speedometer.  I went to a pick and pull and found a replacement cluster, worked like a charm..

That exact same thing happened to me, as well. The problem (for me, anyway.) was one of the dash light bulbs had melted its hole in the cluster. My constantly trying to get it to tighten up tore up the printed circuit that fed power to it, and it eventually caused a short.

Mine, however, blew the fuse for the instrument cluster whenever I turned on the lights.

[bd]

i still haven't found the issue, I've traced every ground and they are all in place and making good contact, any other ideas?

Do this: 
Connect a voltmeter, attaching the positive lead to shiny bare metal on the cab and the negative lead directly to the battery negative terminal.  Have a helper turn on the windshield wipers, dome lamp, etc.  Is there any voltage reading greater than zero?