Bad A/C ground

[Jesus350]

Hey guys so my AC compressor doesn’t engage, im sure its a bad ground since i put ground from my power probe and it engages so i would like to know where should start looking, also this may be related but my third brake light turns on when i press the AC button on and when i turn the AC button off its very dim

 

[RLC2020]

That definitely sounds like a ground issue to me. Start with the firewall ground at the battery and then check the ground at the block. I'm not sure where the ground for the ac is exactly, but it's easy enough to splice in a ground to the compressor right before the plug, that's what I did with mine. Just added a ground to a bolt on the bracket and spliced it at the connector for the compressor.