The gauge should read manifold vacuum direct, the line to the climate control system has a check valve in it somewhere. You could tap into the line ahead of that check valve, or the line to the cruise control unit.

When I installed Volvo cruise control into my 1988 244, I found the best spots for penetrating the firewall (with the vacuum line and wire harness) to be ahead of the glove box. The rubber pad inside had perforations so a round plug could be removed. Easy to pull the glove box and look.

I found rubber grommets at the hardware store with a hole diameter close to the o.d. of the vacuum hose, and the groove i.d. of a drill size that I already had. Once the grommet and hose were installed I glopped them seriously with marine sealant.

So look at the vacuum hoses on your engine. Since yours is a turbo (GLT ?) you may want help from another turbo owner to get the best tap-in location.

Once that location is set, then the hose must be routed into the cabin, and up behind the gauges to the vacuum gauge.

Once in, only the lighting is left to do. Ground to a nearby bolt, hot side use a side-tap into the lighting harness for the central control panel.

The gauge should read highest vacuum at idle, lowest at WOT.

Good Luck,

Bob

:>)

PS: Have you though of a voltmeter?

The only hard part is finding a hole (or making one) in the firewall for the tubing. There should be one in front of the driver's knees for the cruise control system. Or at least a plate to drill through. I've been curious as to whether anything can be run through the threaded holes for the chassis-firewall braces. I'd be more inclined to go out and buy a longer vacuum hose to use a pre-existing hole than to drill a hole to accomodate a short hose.

Once you do that, just put a 'tee' into one of the existing vacuum lines off of the manifold. Don't use the one for the climate control system!

Then all you need to do is wire the lighting. Ground one of the bulb terminals anywhere. Then for the other terminal, just tap into the brown wire that supplies the lighting (or lack thereof!) in the dash behind the center console. A scotch-lock is the easiest way to tap in.

Good luck!
-Ryan
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Athens, Ohio
1990 245 DL 130k M47, E-codes
1991 745 GL 280k (Girlfriend-mobile)
Buckeye Volvo Club

Tap a "T" fitting into one of the vacuum lines running from the intake. If there's an unused port, use that instead. Which motor is it?