99 Blazer's speedo meter, odometer, and cruise control do not work.

What we have replaced:

1) Speed Sensor
2) Instrument Cluster

Still doesn't work.

We also checked the fuses (good).

We think it might be a wiring issue, but can't locate a diagram for the speed sensor.

Also some side information (not sure if it will help, but in-case it could be related) someone butchered the radio wiring in an attempt to add an after market radio and amp. 4 wheel drive also doesn't work (replaced the switch in dash; still nothing). It was suggested we might need a new (topic here) Transfer Case Control Module could this some how be related to the main issue above? Again 4x4 not working isn't a top priority. I only mention it in-case the issues could be related.

Any thoughts, suggestions, or speed sensor wiring diagram would be nice.

 

I would check with a dongle if it can read the speed via OBD. That would at least give the clue whether the problem may be on the cluster's side or not. And, as far as I know, if You loose the signal from velocity speed sensor, Your transfer case is not going to shift the gears. Does it shift normally?

 

Yes it shifts from park, reverse, etc. just fine (an automatic). If you are referring to it auto shifting (1st, 2nd, etc.) than yes no issues there.

 

There are OBD code readers that read codes that do not cause the check engine light to go off. You might take your truck to a place that has one that can read those codes to see if there are any other codes stored that might provide clues. My local O'Reilly's autoparts had one but the Autozone did not.

 

Therefore I wouldn't suspect the VSS sensor circuit is the problem. A speed sensor information, combined with the engine load values determines which gear (1/2/3/4) should be engaged. If You loose that one, the tranny won't shift in automatic.
By an OBD scanner You may lookup the speed value. If that one shows fine, then the problem is more likely with the cluster. The transmission to a cluster, as far as I know, is digital. I don't know the protocol at all, so would be nice if somebody could post the info which of the clusters are inter-changeable.

 

The factory stereo had SCV speed compensated volume. The faster you go the louder the radio plays. If the radio wiring got hacked I'd bet that wire was not capped and has shorted against something. I don't know what color that wire is on your 99 but I'd check it out because the problem is only with the speedometer as far as gauges.

 

Here is your circuit path:

Two wires leave the VSS: high signal is PPL/WHT and lo signal is Lt GRN/BLK

On 4x4 only, these two wires pass through a connector on the top rear of the transmission (C115/8) and emerge as the same colors after the connector then they go to the VCM on C1/P29,30. Two VSS signal wires exit the VCM: DK GRN on C4/P4 and DK GRN/WHT on C4/P3 (this goes through a conn blk and then the BCM)

The DK GRN output from the VCM goes to both the radio and the instr cluster (on A4).

Check the entire signal path and the radio termination.

Happy hunting, let us know what you find.

George