The fuse box is not in the engine compartment. Check below the radio, behind the garbage container.
you can find it in a workshop manual
http://www.volvoclub.org.uk/faq/WaterPumpChange.html
The Chiltons/Haynes 72300 has the vacuum circuits divided into the emissions, Fuel and brakes sections of their manual covering each vacuum hose.
infolinks.com free pdf diagrams... took me forever to find these... be blessed
The engine is not running!
Haynes Repair Manual for Volvo 760/740 has diagrams of the vacuum sub-systems.e,g. the EGR, the ignition etc
On a 240 Volvo (which basically should have the same engine) it is directly under the intake manifold. On a 1985-740 previous comment is right On a 1990-740, driver side, on top the engine between injectors #3 and #4 a big tubing and a small vaccum hose attach to the flame trap
Remove the ashtray. Then lift up and out on the tab labeled "Fuse Box"
You need to replace it. There are 2 screws that hold it on.
in the distributor in the rear of the engine. sometimes known as a hall sensor
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