2004 envoy can i use the cigarette lighter socket to keep the envoys battery charged

If possible, pull the horn relay, use jumper wire on switch side of relay, right side in diagram. If the horn sounds, it's not the fuse. Sometimes these diagrams don't post, for some reason? good luck

As above:)

look inside the socket coin fall into the socket

Fuse number 13 is the cigarette lighter fuse, it is in the engine compartment fuse box on your GMC Envoy. To know more about where each fuse is and what it does, follow this link: https://fuse-box.info/gmc/gmc-envoy-2002-2009-fuses-and-relay

Its common for cigarette lighters to short out and need to be replaced that's my thought they are easily replaced if you don't use it have it perminantly disconnected.

the cigarette lighter probably doesnt work either. check your owners manual for the lighter fuse because that is the same fuse for the scanner connector. should be located either under the hood or under the dash.

If your plug to towed vehicle has an empty prong/terminal, add a charge wire from RV to positive on battery connection to towed vehicle. A lot of travel trailers have a charge line in the 7 prong plug to charge battery on tongue while driving. Be sure to include circuit breaker in line for protection and don't forget end at vehicle will still be live when disconnected from tow vehicle so make sure it is protected from shorting out against metal,other wiring etc.. If no extra prong/terminal on current plug, switch it over to another with enough terminals to accommodate it.

Check the cigarette lighter fuse, this should be in the under hood fuse panel.

2002 ENVOY BRAKE LIGHTS WONT WORK

If I remember correctly if you look at the back side of the fuse cover, it should tell you what the fuses are. Also in the owners manual in the index, under fuses, it should give you a diagram of the fuse location for the acc. outlets. Good luck. The fuse should be a 20 or 25A fuse.