I got a 99 Chevy Blazer in a trade. Here is the list off issues we haven't been able to pin-point or solutions on this forum and other sites haven't worked to fix them.

1) Speed and Odometer do not work. Dash lights come on and all other gauges work. Cruise control doesn't work.
a) We have tried changing the speedometer sensor by the transfer case. That didn't fix it.

2) The Blazer will not go into 4H or 4L. The lights just flash.
a) We tried changing the 4x4 switch as the 4x4 Service Light threw the code for a faulty 4x4 switch. However, this didn't fix it not shifting and the 4x4 service light still comes on. The only code is 4x$ switch code.

3) The dome light doesn't always come on when you open the doors. It does come on if you manual turn the dome light on. It will come on when you first open the door in the morning, but not anytime after that.
a) We have tried just basic trouble shooting.

4) The previous owner took out the factory stereo, but cut wires and left them. This Blazer also has a cassette player that sits below the stereo/AC control (part of the center console). Been having issues finding a wiring diagram.
a) Tried looking in the tech manual, but found no stereo wiring diagram. Also looked online, but none have the diagram for the cassette player portion. We also bought a used factory radio.

Are there any wires we should check for # 1 & 2 under the dash to see if they have been cut or replaced?

Note I'm only assuming it's a wiring issue because of all the issue that may be wire related. Any suggestion wiring or otherwise is appreciated.

 

There is some circuitry for the OEM radio that allows for the volume to increase with engine speed to compensate for increased road noise. So there could be a connection between the radio butcher job and your symptoms with the gauges.

The gauge stepper motors can also fail. I had to replace my gauge cluster because the speedometer needle would "stick" at certain speeds.

I'm attaching some scans from my 1999 GM manual that might help with the electrical connections.

As for the cassette player, there should be a dedicated harness that comes into the general vicinity of where the radio would go on the left side. It is a black plug (it was on mine) that is two pins high and about 8 pins wide.

Regarding the 4x4 issue, it sound like the problem could be with the Transfer Case Control Module (TCCM). Look for posts on TCCM diagnosis on this forum to see if the symptoms match. They do fail after 15 to 20 years. Mine did.

Good Luck!