Wire size?

Hi, I found some burnt wires in the engine bay harness of my Mk1 Esky. There are 3 I need to replace and I need to know what amp wire for each. The coil wire from the firewall, the wire from the coil to the starter solenoid and the horn wire.

Good point with the cheap wire, been caught before. These wires have been replaced before with whatever they had laying around. Cooked the wires and tape.

All the fuses in my MK1 are rated at 8A so you could just go for 13AWG or 2.5mm2 which will do the job. 

If all circuits are protected by 8A fuses I would just trace all the dodgy cabling back to where it meets the original size, then use the blue (2.5mm2) insulated inline crimps to join 13AWG cable. Then take the new cables where they need to go

Where I can I have shortened the wire and will take it to a relay and new wire from there. The others will be a solder joint with heat shrink. I wont be re-tapping it but using a split conduit.

Hi, Most burnt wires have been replaced and a relay for the coil, that part is good. I am having trouble with the horn, I have traced the wire back to a unburnt section and installed a relay with new wire from that point. The original horn didn't work so I used a air horn I had laying around. My problem is the horn works with the ign off or on acc but don't work when its on ign.