melted front lamp wire white/ stripe
 

We have a 1980 450Sl and the body work is nearly complete. While
reinstalling the right front headlamp, we noticed the white wire with
a stripe (can't remember now if it was red or blue because I had trouble
logging into the forum and became frustrated).
Looks like it goes to the fog lamp or possibly directional lamp.
The wire melted all the way up the harness to the bulkhead/ firewall.
Any ideas what might cause this and what the wire is for? Can't find
the manual on disk I bought last year.
Thanks,
Dan