Vacuum Gauge (Fuel Economy) install...

1991 Volvo 240 Sedan, b230, 2.4 LH about 115k miles.

I've got my hands on a OEM Volvo Vacuum (fuel economy) Gauge made by VDO.
It has the following connections on the backside of the gauge:

1) Two electrical connections for the illumination.

2) A nipple of sorts which is to be connected to a tube, a vacuum tube I
guess (There is a snippet of tubing on the nipple and when I suck on the
tube the needle on the gauge moves).

I have a question about the second connection mentioned above. Would
anyone happen to know where the tube is to be connected. Is there a
predetermined place on the manifold/engine, or is a t-fitting needed to tap
into an exsisting vacuum line? Any help would be most appreciated.

Actually while I'm here I might as well ask about the effectivness of this
gauge. Do they actually work? Are they reliable?

 

That connects to any fitting on the engine side of the throttle, which often
requires a tee connector. Look in the "HELP" accessories section in many
auto parts stores.

They do work well to show you the manifold vacuum, which roughly translates
to economy.

Mike

 

Probably the cleanest option is to install a nipple in the intake
manifold into the plugged off port used by the boost guage and overboost
cutout on turbo cars, you could also tee into the vacuum line to the
ventilation controls *before* the checkvalve or if the car has cruise
control that will connect too.