Hummer Ground Points & Accessory Power
Updated October 12, 2009
There are five ground posts with screws up under the dash, against the left side of the chassis. Earlier year trucks have 1 ground point here. They can come loose and cause all kinds of unexplained problems. You will need a 1/2" socket and wobble adaptor to reach all but the first nut.
These are serviced by a large gauge cable so are a perfect place to hook grounds for accessories.
To get to the grounds Open the drivers door and remove the two screws holding the trim piece in the door jamb (above left photo)
Remove the screws holding the lower dash trim panel. Be careful - you will need to unscrew the ODB-II connector (two screws on 96' and later trucks), the floor HVAC vent (one screw into the tube) and the floor light (push on connector - apply side pressure and it should pop off) before you can pull the panel out.
Take a flash light and look up and to the left - you will see a vertical row of posts with nuts (see top right and left photos).
AMG provides a number of accessory connectors under the dash. Some are switched with the ignition and some are always hot. On 98 and earlier trucks these wires are located loose in front of the fuse box. The wires usually have silver labels. Trailer brake wires are also located here.
The left arrows point to the labels, the right arrows point to the shrink tubing on the wire ends.
1999 and newer trucks have a special accessory fuse block which is a nice improvement.