I have a 91 grand marqui I put a new battery cuz the old one tested bad and when I first connect terminals I have power. When I turn ignition to try and start it all power goes out?

you have an intermittent connection between battery and chassis ground (my fifth today, I swear) coarse wirebrush the connection from the black cable to the chassis ground...yes scrape away the paint too...just get to a reliable electrical connection...same too for the cable end....make sure 300 CCA can get thru there~....and connection from chassis to engine too~ Need GOOOD ground....OKAY~

Where is the ground located on the chassis?

well follow the big black cable from the battery...where it ends is the chassis ground...probably has a "Lolli" with a hole in it crimped on end there and is full of corrosion, bout now...hopefully that hex nut isn't chewed off from corrosion~

Doesn't look corroded any other ideas

galvonics are hard to see---imagine a very thin layer....aluminum immediately takes on a galvonic layer reacting with air....the thing is like an invisible sheet that you cannot really see...if you scratched at it with the tip of a screwdriver, you'd see the metal...covered with galvonic corrosion...you cannot see~

I agree with judge. Loosing all power (on a new battery) when trying to start is usually a connection issue. I would double check all connections. Positive and ground.

Real CCA, kinda "smokes" this layer a bit, creating an insulative electrical layer, or WELDS itself in place...if you had any involvement with contacting relays, you'd know what I'm talking about to much juice and contacts simply WELD themselves together...same with black wire pullin' over 300 Cold Cranking Amps definitely will want to weld itself solid~

When I try to start positive side gets hot

Loose or dirty terminals can get hot.

Take it loose and clean battery posts and wire end real good.

Thanks for all the help I got it fixed