Hello, I just bought a 2005 H2 that has 40,000 miles on it. Apparently, the previous owner did not drive it much. The SERVICE 4WD light comes on whenever I turn on the lights. When I turn on the brights, the Trailer light pops on. Does anyone have an explanation? Other than that, the driver door rubs against the front piece when I open it. Everything else works fine.

 

Use something wide and flat, like a metal putty knife..... And pop upwards the door sill plate at the bottom of the front door opening. (If you find a half inch deep of water pooled there, that's your problem.) otherwise, proceed to the plastic trim next year parking brake. Pull in straight back and it will come out. Behind that you will find a ground connection, often corroded and the source of various malfunctions in the dashboard. Take the nut off, closely inspect the ring terminal. If it looks questionable, put a new stainless steel ring terminal in its place, crimp and solder the wire to it. Clean the ground stud to bare metal. Consider going to your local hardware store, and replace the nut that secured it with the stainless steel nut with one of those built-in star washers that really bite in.

Then check the ground connection from the back of the driver side cylinder head up to the firewall. Same thing, inspect, clean and replace has necessary.

People don't often think that battery cables wear out. Well they do, and if yours are original I would replace them both. Pay special attention to where the negative cable bolts to the driver side of the engine block on the driver side, just above the oil pan about Midway of its length. There's also a ring terminal there with a smaller wire. Clean and replace as necessary.

Then get on your creeper and start at the front driver side tow hook. Look just above it into the right and you'll find another important ground with a ring terminal. You have several under the vehicle, exposed to the elements. As you work your way around the vehicle you'll find the ground connections bolted to the bracket that supports the body mounts. One that often gives trouble is right behind the rear tire on the driver side. That one is critical for your fuel pump. You also have ground points at the base of the b pillar.... Save those for last as they usually don't get corroded, and a bit more labor intensive getting to them.

After you're done cleaning these points down to bare metal and everything is reattached, I like to use that liquid rubber in a can ... And completely cover the ground points. (The ones under the vehicle)

While it's easy to do them all at once and get it over with, personally I would do one at a time and see if that clears up the issues.... So in the end you know for sure where the problem was.

I think that's the best plan of attack to start addressing it. Keep in mind that if one module loses its ground connection, it will go back through the harness and through other modules trying to find a ground. That triggers all sorts of codes and bizarre symptoms. Kind of sounds like what you have going on.

And while you're at it, check where the harness goes into the driver's door. You'll probably need to remove the door panel carefully. Replacements can be $1,000 each. Used. You need to get a look at the wires inside that large rubber grommet. It's quite common for those to either break, have insulation rubbed off in short out, etc. the same goes for where the harness goes into your lift gate at the top.

Lol, that should cover 90% of multiple electrical issues popping up. The other 10% are usually related to an aftermarket stereo or alarm that wasn't installed correctly, a problem in the harness itself somewhere, bad ignition switch, and we always save the worst for last.... The body control modules also go bad.

 

Great comment Diaz thx for sharing that knowledge.

 

Wow. Thank you so much. This is incredibly helpful.

 

Lol, sorry I didn't have time to go into more detail about what to do if you find water under that door sill plate :-)

A leak on the roof, or a bad door seal.... And the water pools there pretty deep. Also soaks into the cushioning under your carpet. Gets moldy and nasty, but worse yet you have a section of harness that ends up submerged.... And bad things happen randomly.

 

This is exactly what has happened. There is actually a hole that was drilled to put stereo system in, and it was not plugged, so water got in. I now have to find someone here in Kansas City who can help me deal with this issue.

 

You might fill the hole with the wire through it with RTV. Or the correct way.... Remove the wire from the hole, and get the proper size rubber grommet to fill the hole, with enough room for the wire to pass through it. (Keep in mind wires running through a hole drilled in metal eventually get cut by the metal and short out. Is that what you discovered?)

Or are you faced with that as well as an inch deep of water collected? Submerging that part of the harness in the door still?