So I found where the clicking noise is coming from. It's a box under the truck that's says WABCO
any thoughts
Please advise
Thanks

 

Under the left side of the truck, about halfway along? That sounds like it's the compressor for the air shocks.

 

It's the ABS pump. They all make that sound. I don't know why, but I'm sure someone here does and will chime in.

 

Could be both. If it was originally an SLS truck then the Wabco compressor valves will actuate and run the battery down. You can pull the relays and unplug the compressor to reduce the load. I do remember wiring a jumper on one of my trucks to eliminate the draw. Or you can use a Nanocom to turn off the SLS function and it will not do that anymore.

 

That's not under the truck.