I bought a new CD player for my 2001 Chevy blazer and got all the plugs for it. When I turn on the CD player my outside temperature gauge goes off. I took the CD player back out and put the stock one back in and it works like normal again. Stock radio has second plug to it that didn't connect to new CD player. How can I get everything to work with the new CD player in?

 

Sounds like something has to be wired incorrectly. I'm glad to hear you picked up the harness adapter to get the aftermarket unit connected to your truck. Try it at night and see if perhaps the dash and the compass/temp display are being dimmed way down. There's a possibility you have the dimming circuit (typically orange or orange/white wire in the harness adapter) wired incorrectly or it doesn't like the dimming circuitry in the HU.

If that's not the case then there's likely a power or ground wire that's hooked up to the wrong thing and causing an issue. I've installed countless aftermarket headunits into vehicles over the years and aside from a wiring diagram labeling a wire incorrectly on a couple of oddball foreign cars there's never been an issue with them affecting the other factory instrumentation. Just look a little closer, you'll probably find just one wire that isn't connected to the right thing, it's easy to do.

 

I checked and all the wires and they are connected right
I also cleaned and replaced the ends of 6 grounds on the front frame still didn't work. I put the factory CD player back in got everything back except for my horn.

 

Also I noticed a plug on my truck that goes to the factory unit but doesn't go to my new unit wondering what it is for.???

 

I believe that's for the cassette player but I could be mistaken. My cassette player and harness have been removed for years...

 

Do you know what each wire in the factory harness does? Do you know what each wire going into the new CD player does? Obviously not as you asked about the extra plug.

Seems to me altoncustomtech nailed it when he said you've got it wired wrong. Until you come to grips with that, there is no way to help you. Nothing special about a 2001 Blazer stereo install.