Installing Wideband AFR and Fuel Pressure gauge.

Where's best place to stuff wires through the firewall ?
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Also, best place tap switched IGN power to run gauges for a clean install ?

 

Next the brake booster is a rubber grommet with wires going into the cabin, I went there on my old sierra. I can only assume they used the same spot on the tahoes.

Just buy a add-a-circuit and run it to a 10amp fuse. I don't like splicing wires if I don't have too. Then pick a circuit that is live when the key is, like an IGN fuse.

 

Or an seo fuse... As they are typically meant for accesories anyway... Alot of time when i need a switch power pointi will go to the fuse/junction box under the dash, where the trailer brakes and power seat harness connect.

 

Relay box at your feet has plenty of circuits for HOT, ACC, ground, lights, etc. Put a terminal on your wire and plug it in.