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Oil pressure gauge installation on a Saab 9-5.

This guide is contributed by Philip Durgin.

Glow Shift adapter

The 4 cylinder 9-5 is prone to low oil pressure problems, so I wanted to put in a gauge to monitor the pressure. Hopefully then I could catch any potential problems before the OEM low pressure light would come on (at about 6 psi). Putting the gauge in was easy and only cost about $100, including shipping.
I purchased a 3/4 unf-16 oil filter sandwich adapter, black 7-color oil pressure gauge, and the universal single pillar pod all from GlowShift. This is easier than tapping into the factory oil pressure sending unit and allows you to keep the factory oil pressure warning light without having to add some kind of a junction box.
Filter sandwich

GlowShift recommends the adapter nut be tightened to a little more than hand tight. That didn't feel tight enough to me, so I tightened it a little more than that. But don't tighten it too much or it will distort the rubber washer that comes with it and leak. The adapter has four ports. Because I was only adding a pressure gauge, I plugged three (the adapter comes with plugs) and screwed the pressure sender (the sender comes with the gauge) into the fourth. Use Teflon tape around the threads of the plugs and sender to prevent leaks.
I oriented the adapter so the sending unit was protected by the plastic stone guard. That makes it a little difficult to connect the wires and see the terminal markings, so connect the wires up before installing the adapter. Be sure to mark which wire is the ground and which is the sender wire. I took the ground wire up to a ground terminal in front of the battery; the sender wire goes into the cabin as shown in the next picture.

My plan was to take the sender wire through the firewall, but I couldn't find anyplace that looked easy. But I did notice that the hood release cable comes through at about the right spot. After pushing the rubber grommet back a bit with a screwdriver, it was easy to fish a stiff wire through the hole, and it came out at just the right spot under the dash. I taped the sender wire to the stiff wire, but it was too tight a fit, so I had to drill the hole a little bigger to get everything through. The main problem was the sender wire was now pushed tight up against the sharp edge of the sheet metal. I used electrical tape to make a pad and stuffed it between the sheet metal and the sender wire. If that doesn't hold up, I'll have to come up with a more permanent solution. (DP: consider this grommet under the fuse box).
Gauge pod

To install the gauge, first remove the trim from the A pillar. I used a door trim removal tool I got from the local auto parts place for about $5. The trim comes off easily. I thought the gauge looked best when positioned low on the A pillar. Both the gauge and the pod are light, so I decided to attach everything with Velcro. I Gorilla-glued the Velcro on the pod and drilled a small hole through the trim to feed the wires through. I used double-sided sticky tape to hold the gauge in position. I kept the tape a little loose so I could fine-tune the gauge's position after it was installed.
There's plenty of space at the bottom of the A pillar to feed the gauge wires through. The yellow wire of the gauge is attached to a circuit with constant current and the red wire is attached to a switched circuit that is only hot when the car is running. Constant current is needed because the gauge needs to remember which of the seven colors you prefer.

Rather than tap directly into a wire, I used fuse blades. They go around one prong of the fuse. I don't know if it matters, but I put the blade around the upper prong of the fuse. Before you start pulling any fuses, disconnect the cable from the negative battery post.
Fuse panel

For the yellow (constant) wire, I used the fuse for the electric-operated driver's seat (fuse #25). For the red (switched) wire, I used the fuse for the cigarette lighter (fuse #34). The fuses are clearly marked on the plastic fuse box cover by the driver's side door. Because of the extra thickness of the blade, you have to apply some extra force to push the fuses in. Bend the blades just enough to get the fuse box cover back on.

The green wire of the gauge gets hooked up to the sender wire you brought through the cable hole. The gauge's black wire needs to go to a good ground. There's a grounding terminal behind the dash about 8 inches away from where the sending wire comes through into the cabin.

When the engine is fully warmed up, my gauge shows about 40 psi at 2000 rpm and about 20 psi at idle. There's a little button to press to change the gauge color. I like the green/yellow color during the day, red at night.

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