Hi Roy.
The end of the HT lead goes into the pick up brush holder which is retained by a spring clip arrangement to the mag.
The spring clip is slid side ways to release the pick up assembly from the mag.
The HT lead is held in place with a knurled nut and the end of the lead is beared to the inner wire with termination via a brass split washer.
Very simple arrangement but does corrode and can be cause of running issues.
Check the brush condition and spring condition and clean the mag slip ring. Some replacement brushes offered can be really soft, so if replacement needed use specialist suppliers.