Attention: TDR Forum Junkies 
My speedo became erratic. The T-case needed an overhaul and upon investigation, noted that the speedo gear in the T-case and the sending components were history. These were replaced and the speedo still did not work 
Started to check all of the wiring - could not get any resistance readings from the firewall connector plug back to the speedo sensor. Checked the two wire plug that goes into the speedo sensor - it was full open - even though the wiring and pins appeared in good shape. From the factory, the wiring is just taped and left to dangle in the breeze . . . . it eventually fatigues the wiring at the plug and presto - no signal going to the speedometer on the dash! Repaired the two wire plug and then reinforced with heat shrink, electrical tape and plastic corrugate wire protector and secured so it will not move 
Gotta love these old trucks! Hope this helps someone else. . . .
Started to check all of the wiring - could not get any resistance readings from the firewall connector plug back to the speedo sensor. Checked the two wire plug that goes into the speedo sensor - it was full open - even though the wiring and pins appeared in good shape. From the factory, the wiring is just taped and left to dangle in the breeze . . . . it eventually fatigues the wiring at the plug and presto - no signal going to the speedometer on the dash! Repaired the two wire plug and then reinforced with heat shrink, electrical tape and plastic corrugate wire protector and secured so it will not move Gotta love these old trucks! Hope this helps someone else. . . .
