Is your 850 10v or 20v car?
10v cars were not imported in U.S.
B5252 is 10v car.
Is CEL on?
Read the codes from A2 and A6.
'93 non turbo have two separate ecu(s) for engine(A2) and ignition(A6).
You have built-in diagnostic ports under the hood on ecu box.

The bearing on the tensioner pulley have protective membrane(seal).Wd-40 couldn't get into it without dismantling. If you want....you can remove tensioner arm,it is bolted with 2 bolts to the engine and then remove the pulley which is held with big torx bolt....but first release the tension and remo...

IAT sensor have exactly the same spec as ECT.
Multimeter is all you need.
A2 5-1-2 :
https://www.scandcar.com/volvo-850-error-codes/

You have a vacuum leak somewhere or o2 sensor connector is bad.
FPR-fuel pressure regulator should be checked if it leaks fuel into vacuum line.

Just regular red ATF...1l is enough for power steering.

No lighter!
For Map you measure voltage while applying a vacuum to it's vacuum line and voltage at rest.
YouTube have a lots of videos on how to check Map sensors.

For IAT you measure resistance,just like for ECT.

The easiest way to check compatibility is to remove the bulb sockets from right side for warning lights and with a help of flashlight to check if it have ETS light(that's for '99 & '00).

If it have Lambda symbol it's for '97 & '98.

Fog light from the 1st picture is for '92-94 850.
They have different bumpers(headlights,side lights,tail lights...etc).

2nd picture with fog light in the bumper is round fog light(spot light,projector) for '95-'97 models.

There is no fuse for it.
It illuminates along with cluster and other dashboard and center console lights when you turn on the headlights switch.

Vacuum leak is your problem and spark plugs if they are not cheap Bosch copper plugs properly gapped. Gap is critical on turbo engines. That leak is messing with Maf and o2 sensors readings which results in higher fuel consumption. In stop and go traffic with short distances...add there automatic tr...

After you replace the hose and correct gap(if it's not gapped correctly),remove negative battery cable for 15min to reset fuel trims.