lighting trouble

[180fan]

Ok here's the situation. I've got a 89 240sx and it's got a lighting problem.

When I turn on the turn signals (with the headlights and illumination system off) both turn signals turn on and the lighting in my car stereo blinks.

When I turn on the illumination (with or without the headlights on) both turn signals stay on not blinking without activation. When I try to turn on the turn signals or emergency blinkers, they click once but nothing else happens.

I've checked the bulbs for double and single filaments, they're all ok, checked the relays, the time control unit, the combination switch, along with the various switches around the instrument cluster. They're all working fine.

I suspect it could be either one of these1. main harness running through the cabin of the car to the rear2. the instrument cluster

The reason I suspect the cluster is because I'm pretty sure I've got a short in there as my "Brake" light is always on, but when the RPM's rise around 2k, it'll buzz and go out then come back on when I let off the throttle.

Any other suggestions on what to check before I go through quite a bit of work to get the cluster and test that out or the main harness?