Speedometer doesen't always work . It will starting working then will quit.

Output speed sensor usually located in transmission usually close to where axles go into transmission. The sensor can be identified by having 8 mm headed bolt that hold the sensor in. These speed sensors just don't quit one day. A wire is usually the culprit or debris on magnet of sensor or physically broken sensor. If speedometer intermittently starts working then its always a wire with bad connection.

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its located on transfer case rear end near propeller shaft , have 3 wires plug

sounds like a faulty speed sensor check you electrical connections at the sensors as well as the transmission is the check engine lite on

could be the VSS - vehicle speed sensor .
Speedometer and Odometer
The Vehicle Speed Sensor (VSS) is a gear driven permanent magnet generator. The vehicle transaxle houses the VSS. The VSS generates a sine wave output with a frequency proportional to the vehicle speed.
The Powertrain Control Module (PCM) converts the CKT 389 signal to an output that switches to ground at a frequency of 4000 pulses per mile. The CKT 389 signal drives the speedometer and the odometer. Various other vehicle components use the CKT 389 signal. Refer to Engine Controls.

The odometer quits working when the speedometer quits working. The most common cause for the speedometer to quit working is the speed sensor in the transmission. You said you replaced it, there is also a transmission speed sensor on your truck that may need to be replaced. I understand your frustration, but there is nothing else that would cause the speedometer to quit except the cable behind the gauges being clogged.

When the gauges quit, does the ABS light come on? Does the gas gauge and temp gauge quit too?

check your speedometer cable, unplug it from the transmission and replace it, that should take care of it.

I installed and after market stereo and my speedometer quit working 1999 chevy s10 blazer

It maybe the speed sensor that sends the signal to the speedometer or the speedometer itself that's has a short in it.

Unless it is a wiring problem somewhere, then I would guess that the two problems are separate issues and they just happened to both go around the same time. I am still thinking that the horn issue is probably just a fuse. The speed sensor is not as bad as it sounds, and it is actually pretty easy to replace if you know where to look. The speed sensor can be purchased from any honda dealer or chain auto parts store. I would always recommend genuine honda parts, they are a little more expensive but are much more reliable and are always an exact fit. If you would like to change the speed sensor and need help with that, please let me know. You can e-mail me at [email protected]. Thanks, and I hope this fixes your problems.