My MGB GT

I had a mystery yellowish wire on the car going out of the bundle close to the alternator but not connecting there for sure... My '75B has always been running well (daily car) so the fact this wire is not connecting to anything obvious kept bothering me. Here is the wire, yellow with a red lug attached:     After precious help received from http://www.mgexp.com , this wire is in fact... not used on my car, with the current engine (Gold Seal engine, numberBHM 1111 471, even if it is not golden painted...). Normally this wire was used on older model for the oil pressure sender, as shown on the '69B from Richard there:  

On modern car, usually a buzzer warns you when you leave your lights on while leaving your car. Unfortunately on our oldies, such devices were not always available. That could result in a discharged battery... After having left a couple of time the lights on (but been lucky enough to not have a completely flat battery when returning some hours later), I have decided to install a warning buzzer. Theory: I am using the wiring diagrams from  Advance Auto-Wire  (document  here ). My MGB GT is a 75 UK model. The correct wiring diagram is the one on sheet 31 (page 32 of the pdf file). We want to add a buzzer that detects the parking lights are on when the door is opened. That means we need to connect a buzzer between the parking light feeding wire and the door switch. The parking lights feeding wire is a red & green (RG) starting at the "HEADLIGHT SWITCH", the door switch wires are the purple & white (PW) "COURTESY LAMP & DOOR SWI...