Repair dodgy electrical connectors
Take a picture
Check for signs of corrosion in places like copper wires, as well as burn marks or melted plastic. Photograph it before you start. If the connector needs to be replaced, cut off with 5-10mm of wire showing.
Strip and crimp
Use stripping pliers to remove insulation and cut the wire. If done manually, score it before stripping. Next, run insulation sleeve over the wire. Crimp loosely before going down a size for a firmer connection.
Heat it up
Use an automotive solder in the ignition circuit. Get the area just hot enough to drip-feed flux into the crimped area before sliding the insulation up. Next, you need to heat shrink it with a hairdryer.
Give it a spray
Intermittent faults that only show up with a when it’s wet can be tracked down using a plant sprayer with a long nozzle. To test for a fault, drench suspect connections like plug caps and fuel injectors.