Headunit problem

Need a bit of help!

Tried fitting a new head unit to my 89 cabby as it didnt have one when i got it, plugged everything in as normal but nothing happened! Then looked at the loom and realised that the yellow cables were in different terminals so swapped them over to match plugged it back in and the unit powered up but no display or anything else worked. Tried to reset the unit and that made no difference either?

Is there something im missing?  

Also there is a blue wire on the car loom that dosent connect to anything on the unit, is this for a power aerial maybe?

Hi

Iso radio wiring for power is as follows

Yellow- permanent 12volts

Red- switched 12volt feed

Black- Earth

Blue- 12 volts when radio is switched on, feed for amplifiers/Electric aerials

Orange- Connect to dash illunination circuit

and vw wiring is like so:
red - permanent live
brown - earth
brown/red - key in ign feed (not always fitted)
blue/grey - dash illumination
yellow/white - speedo signal


sounds to me like you may have tried to plug the stereo power into the speedo signal wire? if so that wont work
if your car has the brown/red wire great, connect red wire from stereo to that, and yellow wire from stereo to the red wire on the vw plug.

if you dont have a red/brown wire, plug both the stereo red and yellow wires to the vw red wire. most stereos have bullet connectors which allow you to do just that