Speed sensor wire from dash

NoDOHC · 03-27-2011, 08:19 PM

How does the digital dash know your speed? Is it reading it from the ECU?

If so, you may have to splice the wire. It is not a very big issue, as this is not a high frequency signal.

Most speedometers are 4,000 pulses/mile. At 100 mph (not that you will ever go this fast

), you will get 400,000 pulses per hour or 111 pulses per second (111 Hz). This is well below the speed where you will have to worry about any transmission dynamics of the wiring (typically around 20 kHz). Correct wire impedances and termination are not necessary at that speed (although I would recommend twisted-pair wire and probably a shield).

vex · 03-27-2011, 09:39 PM

Quote:

Originally Posted by NoDOHC

How does the digital dash know your speed? Is it reading it from the ECU?

Yes, it's pulling it from the ECU.

Quote:

If so, you may have to splice the wire. It is not a very big issue, as this is not a high frequency signal.

Most speedometers are 4,000 pulses/mile. At 100 mph (not that you will ever go this fast

), you will get 400,000 pulses per hour or 111 pulses per second (111 Hz). This is well below the speed where you will have to worry about any transmission dynamics of the wiring (typically around 20 kHz). Correct wire impedances and termination are not necessary at that speed (although I would recommend twisted-pair wire and probably a shield).

I'm looking to avoid the wire splicing (i'm anal about that). There looks to be a software upgrade in the pipeline which might be able to do what I want.

03-27-2011, 08:19 PM	#1
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 17	How does the digital dash know your speed? Is it reading it from the ECU? If so, you may have to splice the wire. It is not a very big issue, as this is not a high frequency signal. Most speedometers are 4,000 pulses/mile. At 100 mph (not that you will ever go this fast ), you will get 400,000 pulses per hour or 111 pulses per second (111 Hz). This is well below the speed where you will have to worry about any transmission dynamics of the wiring (typically around 20 kHz). Correct wire impedances and termination are not necessary at that speed (although I would recommend twisted-pair wire and probably a shield). __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)