The poster who suggested putting dielectric (non-conducting) grease in the connections is correct. If you take apart many connectors on a new car, you are likely to see grease.

When I had some mysterious electrical issues with our '90 744 TI, I did one connector each week - that way if something happened I knew what to check.

Clean the connectors as much as you can, and if you have any trouble, look inside each male and female connector to see if any pins have been pushed into the connector.

The old gag is - do not put anything in your ears except for your elbows!

I never use a washdown on an engine.

I clean my engine with an old sock - I use a spray bottle of kerosine for metal parts and a spray bottle of soapy water on rubber or plastic parts, drying everything thoroughly. If you wear a nitrile glove, you can turn the sock inside out when it gets too dirty.