Now and then you read about electric components acting strange. Here is one example from my 412. When the engine is cold, wipers, washers and brake lights, (stoplights) dont work. Fuse is good and I have current at the fuse. After driving 5 - 10 minutes, everything works, which means that whenever i get to my mechanic who is close by, all is OK!
That sounds quite true, I'm somewhat puzzled though as the electric board is situated inside the car and doesn't receive much heat, and I have voltage at the fuse even when cold. Could there be another location somewhere in the engine bay where these three functions join?
You'll need a wiring diagram to find all the connectors in the system. Some signals go through three or four different connectors, along the way. It does seem odd that the wipers and brake lights would go the same direction. I can't say on the 412, but a number of the connectors on my 328 are undersized for the current. I had an intermittant I finally tracked down to a burnt edge connector at the relay panel -- the plastic shell had deformed under the heat, and the connector was moving around inside the shell. And those Bosch relays put out a lot of heat, too.
It could be a coincidence but I'm betting that you'll find a common place where all these devices get power that has an intermitent (possibly corroded) connection. Board edge connector, harness plug, etc. Don't forget to check, clean and tighten any grounds.
Yeah, the tach on my 400 doesn't work until it gets warmed up. I can tap the top of the dash and it will come on, otherwise I have to wait 10 min or so.
Since the wiring on these cars is so complex, you may want to do what I did: Get the manual on CD-ROM if you don't already have it (and if it's available for the 412), take it to a reprographics place and have them make you a blueprint-sized copy. It cost about $10 for two copies and it makes the wiring diagram much easier to trace. You could even get it laminated and then trace circuits with a dry erase marker if you really wanted to get fancy. Intermittent electrical problems are probably the most frustrating problem a car can throw at you. Like the others said, I would look for loose or corroded connections first.
I would suspect an intermittent ground somewhere, that would account for multiple systems having the problem. If there is oil on a ground connection or junction, it would tend to thin out as the car warmed up, even a little temp change could make a difference. Certain types of corrosion, like battery electrolysis born, would do the same and even feel a little slick to the touch. As current passed through the connection it would attempt to find a path of least resisitance. Until enough current is allowed to pass nothing will work. You will still be able to measure 12 volts on the meter because the meter will operate on microamps or milliamps. As mentioned earlier by the gentleman with the 328, mechanical problems with a connector are also a possibility, but I would look at the grounds first.
