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Thanks for posting
The original speed sensor in the 5 speed sends a analog wave form to the speedometer the speedometer then converts it to a square on/off signal that the computer can identify and use as input. Your gps sensor probably has a digital output, the speedometer can not use this. The only solution possibly is to wire the gps directly to the speed input wire on the computer but your speedometer odometer will still not work because it needs an analog input.
I'll have to check a wiring diagram for the wire color and position on the ECM and get back to you.
Click on this link, the spd input wire for the ecm is on connector E3 terminal 22, it is a white/red wire.
Good luck with that, it seems everything is digital these days, Toyota later went to the system where each wheel has a speed sensor which are square wave and these go directly to the ecm and then to the speedo, sorry but that's about all the help I'm gonna be with this , best of luck.