Need Help Speedo reading very incorrectly

[Slipady]

Speedo is reading 15-20mph ish too high

Hi there, after swapping my my bike to an fz8 Speedo to my 2005 fz6 by splicing the same colour wires together due to my harness being OEM but different?

Most online posts talk about a simple subharness swap but mine doesn't have that, my harness having the part number: 1b3-82590-00
And others having the number starting with 5VX

Any way after riding to and from work today the speed was displaying 45mph while I was riding with the flow of traffic so 30mph give or take and was displaying the temperature as in the 90's while moving after 15 minutes of riding.
I was wondering what could potentially be causing this and is there any suggestions?

 

[Motogiro]

Welcome to our great forum!
Normally the speedometer can show a percentage error. Your error sound like it's greater than average. Many people install a speedo healer.

 

[Gary in NJ]

30 mph is 48 kph...is it possible that your speedo is displaying in km?

 

[Slipady]

30 mph is 48 kph...is it possible that your speedo is displaying in km?

I checked that and switched it to kph still the same issue