The engine is running and when the headlights are turned on the wiring under the dash starts melting the rest of the loom what could cause this?

check under dash fir loose wiring loom. Check under hood too where steering rack is. Somthing is pulling the loom to cause this.

Sounds like a wiring harness problem. Sometimes your wires will get very hot and melt themselves together. Pop your hood on your car and look at the corner closest to the drivers corner under the hood. A patch of wires should come out. check them for any melted wires. Also look under the dash of your car for any melted wires.

No - the worst electrical problem that the headlamp harness could cause is to short itself to ground somehow (bare wire, unplugged & turned on, etc), which would blow the headlight fuse.
However, dashboard problems can cause headlight problems, since the headlight switch is located in the dash.
The common point between the headlight problems, dashboard problems, and "electrical problems" would be the under-dash wiring and/or wiring harness from ECC (Engine Control Computer, aka "the car's computer) to the dashboard - check here first for grounding/shorting problems, or water leaking out of the in-dash vents onto a wiring harness.

Hi,
I'll make it brief( something wrong w/ my ISP ).
You got problem in the light switch assembly, the plastic cam is already melted and failed to push the metal contactors to the contact points. Replace is necessary.
The brake and headlight problem, better check the shorted wire in the relay and fuse box in the engine area, there is a shorted wire that stealing the power of the headlight relay, thus it turns off when you step on brakes.

Recommendation: Better have a tech to check on that, a total check up of the lighting and brake light harness is required, the main harness under your steering must be check thoroughly.

Hope that helps!

look for large wiring loom under steering column that is patch harness going to immobiliser module,
two black large connectors that look the same disconnect and isolate connect original loom connector from top to bottom body harness original connector and presto no more immobiliser its bypassed vehicle now works.

Have you tried wiggling the turn signal lever when the problem occurs? I have seen multiple cases where the wiring inside the headlight high beam/turn signal switch melts and causes the problem you are describing. If you can wiggle the high beam/turn signal switch and CAUSE the problem, you have a defective high beam/turn signal switch.

check if the wire on the starter is fallen off or burnt.It might be touching on part of the chassis or engine and shorting when you try start the car.Is the engine turning over? Put the car in 3rd gear and try pushing it to check if the engine is not seized.If the engine is seized the starter wire will heat up as the starter will not be able to turn the engine.

Sounds like you have a short to ground causing your fueses to blow. These can be difficult to find at times. You will have to look around for wires that are grounding out on the frame or on another wire. It could possibly be found in the engine compartment. Move wires around and start looking under wire looms and such. Good luck....

sounds like either a wiring loom is shorting across somewhere ??where ----best of british to finding it

check the back of the bulb to see if its damaged,melted then check the relay and the wireing loom for broken wires