Here are some tid bits I placed on my website to let guys know the importance of the Grounds in relation to Buick's Plastic Dash Bezel . . . . . . (This was in relation to the Headlight Switches but does mention the importance of ground the Gauge Hosings as well) Copied and Pasted from my website . . . . . Note: Because Buick’s use a Plastic Dash Bezel these switches must be grounded. You can use the factory ground Buick provided OR you can use the built in Ground Spade that this Switch provides as well. This is a nice feature most other aftermarket switches do not provide. Photo below shows the Factory Grounds for the Headlight Switch and the Wiper Switch. These should be in use for each switch to work properly. Each one shown here installed correctly There is also a Jumper Strap located between the Speedometer and Gas Gauge to help ground the Gauge Pods! (Housings) The Gauge Pods need to be grounded as well (In most cases the Lights in the Gauges won't work unless the Pods are grounded) Photo below shows the “Extra Ground Spade” included in our switch. This Extra Ground Spade can be used to ground the headlight switch to the chassis.
You can wire in your own grounds if you want to make double sure everything is grounded. Here are some photos of a Dash we recently "Grounded" with our own wiring . . . . . You'll need some wire and some eyelets to crimp in place. Then simply attach the wire to a good spot on the "Metal" Dash Area or Chassis.
I highly recommend the extra, dedicated grounds added like Todd mentions above. The 3 gauge pods share ONE ground off the speedo...
When I replaced the bezel in my car 2 years ago I added a daisy chain of grounding straps with star washers and dielectric grease similar to what Todd recommends. Along with LED lamps and fresh lenses I highly recommend the exercise. Its something you see and appreciate every time you get in the car and every time you look at the speedo or tach.
