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Re: LSx swap Speedo ?
Its because the PCM puts out a 5v square wave signal.
your aftermarket speedo is looking for a slightly higher sinewave signal.
the guy with the harness and PCM tuning ability would always want you to use the PCM wire, because it give him full power to change the output to the speedometer. he can tune it for gears, and he knows the PCM is getting the proper VSS signal.. this is important for some small things, like fans.
since its aftermarket, and can be "programmed", the gauge company will suggest connecting it directly to the VSS. they arnt used to talking to people that can program their PCM output signal, and have provided their own calibration method.
options:
1. you can build a small simple circuit to round off the square wave.. you might also want to do a 'pull up' circuit at the same time to raise it from 5v to 12. this would be my solution.. but im also another guy that can use/program the PCM.
2. SPLICE (not cut) so that the VSS signal goes to both the PCM AND the speedo... this is the easiest option.
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