1989 3.0 base model 4x4 5 spd, no a/c. Popped code 42. Possible fixes vs ( whatever that is) wiring or ECM. My question since this has to do with vehicle speed, foes the ECM get its days from a speedometer activated source or from something electronic? In other words, do I need to go ahead and replace my cable?

 

IF you have the cable-driven speedometer (I'm pretty sure you do), VSS1 is a reed switch mounted inside the combination meter (speedometer). That provides the speed signal to the ECU.

So if your speedometer is not working because the cable is damaged, yes, you need to fix that.