In the 1989 Volvo 740 GL with a Bosch system it is located just above the steering column on the dash.
Not necessarily, most do however.
under the left hand bumper
behind the fuses, below the radio, behind the lowest box in front of the shifter.
i have a 1989 740 and mine is located on under the hood it the green 1 on the side next to the air filter
Fuel pump relay or Knock sensor if stall after maybe 2 miles
2
There are several things that can cause your 1990 Volvo 740 to stall while driving. The most common cause is a bad fuel pump.
Try overdrive relay, you can buy them anywhere, replace old one, it is very easy.. I had to replace one on my 88 740. Give it a shot before you let someone work on it.
change the overdrive sensor should be on the left side of the gear box.
Yes. However it's not that easy due to the turbo versions electronics (if it's a 700 series turbo your after). But fully possible and has been done several times.
Volvo recommends using a synthetic oils that is 30/5. They have 30/5 oils for vehicles over 150k miles that work just fine.