I just installed a amp and when wiring it up to my sony head unit I needed to check an existing wire conector and I somehow blew a fuse. I have changed the 20amp fuse but nothing won't work I've checked all the fuses in the car under the bonnet.Ive disconected the amp and have even tried a different head unit and still nothing what have I done? also the over speed indicator won't light up.
I"ve got no idea whats happened.

have you checked all the fuses under the steering wheel? next to where your accelerator is?

Yes checked them all I'm still scratching my head.

Fuse within the amp?

The fact that the speed indicator has shut down and the amp doesn't work im going to say double, triple, quadruple check the fuses, check ALL the ones in the kickpanel with a torch and then the ones in the fuse holder in the engine bay (there should be one or two in the yellow partition which are prone to it.

You can never check them too many times, and I really doubt you have blown anything else than a fuse.

And please next time disconnect the battery while working and check every connection prior to refitting.

Fuse within the amp?

My bet is that those ones will be on the exterior of the amp, so very easy to check aswell.

Check the fuses in the yellow holder in the engine bay fuse box.

Thanks for all the help but as I have said I have checked them all even the amp will have to wait till Friday afternoon I only found one fuse blown a 20amp may just have to change them all.

may just have to change them all.

Thats not going to achieve anything, disconnect the battery and check them all, no need to replace them all.

pull every fuse out if you have to and check with a multi-meter. it may have a tiny crack you cannot see, believe me it happened to me!

The multimeter is your best friend when it comes to electrical fault finding. Each fuse has a tiny exposed bit of metal on it so you don't have to remove each one to test it. Just set the multimeter to continuity and start checking.

Just noticed this was from a couple of weeks ago... sorted it out?

And when you say "nothing won't work" that's a double negative which means that everything does work. :)

If anyone is reporting a problem like this, it might be good to be specific about what does and doesn't work - is it only the stereo gear that didn't work, or does the car not have electrical power anywhere?
yeah, it's been a number of weeks, I'm sure it wasn't that bad. Hope it's all sorted and you've been able to enjoy your music!