well the problem is that the speedo is beeing sodlered leadfree so you need to get a mixture of leaded solder wire and the unleaded one on the solder tabs
I used a ersa RDS80 digital or now the GM soldering station to resolder various ESCs
not an issue really, you just need atleast 450° and a proper soldering station
easiest way to get the wires replaced, and the safest aswell, is to send the speedo to GM
do not!!! remove any part of the case!