I have a really odd issue with my GQ.

I’ve just had bigger wheels/tyres fitted (285/75/16) so booked the car into a gauge place to have the speedometer recalibrated.
After picking up the Patrol I noticed the tachometer needle jump when i released the handbrake to drive off.

Anyway, further down the road i pulled over to go to the shops and when i pulled the handbrake lever up the tachometer was reading 0 RPM with the engine still running. So i then lowered the handbrake lever back down. With the lever halfway down the tachometer was reading 650RPM (which is what it idles at). Once fully down the tachometer was now reading just under 1000RPM. At no time during this happening did the engines ACTUAL RPMs change, just the tachometer.

I rang he gauge place and explained the above with his reply being “was it doing it before you dropped the Patrol in”. I said no and if the tachometer was doing that then I’d have got him to recalibrate the speedo AND fix that since i knew he would have removed the dash cluster anyway. He said he just took the cluster out and removed/attached “about 3 wires”.

Does anyone here know why the handbrake lever is affecting the tachometer reading when the only apparent thing is the dash cluster being removed??? I’m stumped 🤔