HELP!!!!

I am working on a 1998 Chevrolet Topkick, C6500.... It has a 3116 Caterpillar Diesel, and a 7 speed Spicer trans....... I am having problems with the Speedometer, and Tachometer.... They have never worked, and Im not sure why...... I didnt care until MSHA told me that the mine trucks have to have working gauges..... all of them..... so, I am needing to find wiring diagrahms of this truck........ I have replaced the gauge cluster, and it didnt change anything...... All the other gauges work, minus these 2......... Im needing info on where to find the speed output sensor, and where the tachometer ties in.....

Tach should be on top behind fan hub or around front cover and speedo should be in the bellhousing.

Okay, that helps...... do you know of anywhere I can find the schematics for this truck? I have 5 of them that I take care of, so it would be nice to have them......

PM me an email or something and I can send them to you monday. I have 2 of the topkicks and I have all the service/parts manuals for them. They are on my shop computer or I have the actual manuals.