Here is one thing I have been seeking to resolve. Same 5.8L 351W 4 barrel carburetor engine.

This engine has three ported vacuum switches. One is a four port switch and two are three port switches. The mystery is identifying which two port switches should really be installed in my engine. I have called Ford but they say my van is too old. They no longer have detailed information to determine what should be installed. All they would do is replace what is already in the engine with identical parts.

Here is the dilemma. Both of the two ported vacuum switches in my van are the same color: yellow. However, they operate systems that require opposite responses.

1. one operates the distributor advance. As far as I can understand, this switch should respond to overheating. When the engine overheats the switch switches controlled vacuum to a direct vacuum source to advance spark and accelerate engine rev. This promotes cooling.
2. the other operates the exhaust heat control valve. This switch should respond to temperatures lower than operating coolant temperatures. When the engine is cool, the switch sends vacuum to close the heat control valve. When the engine warms up, the switch stops the vacuum.

I have concluded that a yellow switch appears to be the right one for the distributor advance, but I don't know what color should I use for the heat control valve. Right now, with the yellow coded switch, the only time the heat control valve closes is when the engine overheats. That's the last thing I need.

Anyone has a working system like this or knows which colors should I use for these two ported vacuum switches?