purple/white wire melted

hello,

I installed a new starter motor on my 1100cc mk1,
the starter motor turned over but did not run on after but cut out  even though plenty of fuel going unto the carb, I notices the Coil HT lead to dizzy was not secured at the dizzy end, and the purple/white  wire  (factory piggy backed with the black wire to the starter motor) started to melt from the coil towards the fuse-box inside the loom to.

now then, I chased the p/wh wire all the way to the white connecter plug in the fuse box, and notice all the wires from the screen wiper are in the same white plug,and looking in good order. all the fuses are in good order to.

when turning on the ignition key ro first position, the screen wiper starts moving whit out even using the stalk wiper lever and will not turn of until you turn the ignition key to the off position

I can now easily replace the p/wh wire but what can the cause be, was it the HT lead not being connected properly?can anyone point me in the wright direction, was it the coil that packed up….?

many thanks