Mazdatruckin.com has a schematic for the B2600i vacuum lines in their tech section, it includes 4wd and cruise control devices. See the attached links below.
Under the drivers seat
where dose the vacuum under the battery come from
Right under the intake manifold. Above the starter. Tucked in there you will see a yellow/red wire leading right to it.
There is a sticker under the hood somewhere that will show you where thay go.
Diagrams are usually located on a sticker under the hood. If not, get a motor manual with vacuum diagrams in it.
The vacuum control valve releases pressure in the float bowl under hot driving conditions. See the links below for additional information.
I just popped mine out on a 1990, I hope. It was only about 30 Fahrenheit, I think. Anyway, the fluid is pouring out of a round hole under the drivers side exhaust manifold. All I had to remove to see it was the cowling. Wish me luck and the same to you.
By the vacuum assembly. Look on the hood or somewhere under the hood / engine compartment for a schematic, or just pull it up online or in a Haynes repair manual
The main relay is in the fuse panel located under the hood on the driver's (left) side. Original equipment relay is green. Schematic decal is on the inside of the fuse box cover.
You may have a large vacuum leak, Check under the hood for disconnected or cracked vacuum lines.
The PCV vacuum supply hose is located under the intake manifold. It is not uncommon for this hose to tear and create a vacuum leak. Removal of the intake manifold is needed in order to get access to this hose as there is not enough room to get hands or tools into that small area.
If the vacuum line diagram is not on a decal under the hood, or, if you don't know anyone with a similar vehicle that you can compare with, try your local public library's reference section on vehicle repair. Reference books are not available for checkout, but you can make copies to take home with you for reference.