Electric system question

[Fleurya]

Hi Guys, I'm a new Hmmwv owner and thanks to all the info on this site I've been able to solve some issues but electric system is not my forte. I bought a grounding harness and got it on the mail today. Looking at my vehicle I just realized that there is no grounding cable to the smart box... could that be the reason the wait light blinks for a millisecond and then goes off? could this also be related to the non functional oil pressure gauge and voltmeter? the fuel gauge is on empty and when I put the switch in the run position is goes all the way to pass full... could that also be related or if it was a grounding issue that fuel gauge would be bellow empty like the other non functional gauges?
Planning to install new grounding harness and a brand new smart box tomorrow.

 

[Action]

The box ground is in the harness plugged in it. The harness you bought will attach to one of the mounting screws.

 

[papakb]

The grounding harness makes up for a lack of good electrical bonding in the HMMWV caused by the way the body is put together. It's purpose is to make sure there are no potential differences between the power train, vehicle electrical system and instrument cluster. One of the biggest sore spots is the ground stud that goes through the firewall behind the heater controls. It can loosen or corrode over time and when that happens the gauge panel loses it's ground reference and the gauges start doing all kinds of strange things. The fact that you have multiple gauges not working points in this direction. On the back of the instrument panel is a 5 lead harness that feeds DC power to the gauges. It's also a common failure point that you might want to check. The fuel gauge issue sounds more like the cable to the sending unit in the tank is open. And who knows what some 18 year old in the military did to your truck!

When you work on the electrical system in the HMMWV there are a couple of things you always want to do. Disconnect the batteries before changing out components like the control box. There's sensitive stuff in there that can die if you don't. A good disconnect switch in the ground lead of the batteries does a good job of this and can also be used as a theft deterrent. Use a good quality switch as there's a lot of current that runs through it. Do not used one of those green know switches, they burn up! Marine supply places are a good place to look for them. Another trick is to use an anti-oxidant grease on all of your electrical connections. It's available at any electric supply house and places like Home Defect and Lowes.