In a quest to fix my jumpy speedometer, I began yesterday troubleshooting the usual suspects of grounds, speed sensor & wiring. I checked all the grounds and they were tight and clean, so I moved to the sensor which I had already bought to replace anyway. While under the truck I noticed the wiring was in bad shape that ran towards the firewall - a white/orange stripe wire and a black/blue stripe wire. I traced them to the drivers side of the motor where the white/orange ran into a harness about the size of a large package of gum and the black/blue ran directly to the oil pressure sending unit. I unhooked the plug from the oil pressure sender and got my volt meter out and tested for resistance and its for sure that wire as there was some question if I had the correct wire.

My question is this - these wires are in bad shape and I think the cause of the speedo problems so where should I splice? I was thinking right at the harness for the white/orange, but the black/blue threw me way off going where it went.

Any help/explanation would be much apprciated.

 

Forgot to another question - if the wires are bad, then how can the oil pressure sending unit be sending the correct pressure reading to the gauge if its utilizing the same wire.

 

Not sure that I followed your description , but many sensors will share the same 5 volt reference for the sensors [ they all need power to work ] .
Also what do you mean by bad shape , if there are a bunch of them , you may want to go to a junk yard and find a good harness .

 

Sitting here thinking I figured it was a shared voltage source but was not sure. The only ones in bad shape were the two coming from the speed sensor - right where they go up against the fire wall they were cracked and split so I am just replacing those two wires.

 

The blue/black is the sensor ground.

Bad connections will mess up the speedo reading for sure, the voltage on those wires is very low.

 

After working with my volt meter I wished I had never even posted such a dumb question.

However, just to clarify, my problem was the plug that goes on the VSS was loose and not making a good connection plus the wires to the firewall were in horrible shape. I got a new VSS that had an adapter harness on it, so I cut it in two, used the plug for the VSS and connected my wires there. That took out some of the craziness but then replacing those wires to the engine compartment solved everything.

Just thought I'd share in case someone ran across this while searching.