replaced rotor sensor..still no speedo?

[mr wayneker]

yeah I bought and fitted that very same bit on Saturday....still no good

but when out on it last night all of a sudden it came back to life then died of when I put the lights on
so played around a bit..lights on..lights off....then lights off and it steadied for a bit

then noticed when I put the brakes on it spiked??????jumped 5mph every time I put the brakes on??????

so now I don't want to invest in the speedo cable...should I get the electrics checked???