Adding a rear fog lamp; adding a relay holder

I'd be interested in a write up if you're up to it.

 

I can get you a diagram and some pics this evening.

 

All-righty. Here we go.

Materials:
- Headlight wiring harness, NAPA Part # TEE HWH101
- Low-profile fuse holder tap, ex: NAPA Part # NW 785170
- 7.5A low-profile fuse
- Butt splices
- Hot glue sticks
- Split-loom tubing
- Standard automotive relay and accompanying socket
- Primary wire, 14-gauge, both red and black

Tools:
- Wire cutter/stripper
- Splice crimper
- Hot glue gun
- A small vise is a handy thing.
- Multimeter

Diagram:

Process:
- Acquire the wiring harness, cut it in half, and discard the black tubing. Strip all four wires for use with splice.
- Cut about 6' of the red and black wire and strip one end of each.
- Crimp a splice onto each of the H11 Male wires.
- Twist the red primary wire together with the red H11 Female wire. Insert that into the splice on the red H11 Male wire, and crimp securely.
- Repeat the above step for the black wires.
- Use the hot glue to seal the open ends of the butt splices. Use the vise to hold the splices while you apply the glue.
- Use the split loom tubing to cover your newly-modified harness. Tape the splices together, if desired.



The pic above shows a connector at the "long end" of the newly-modified harness. Ignore that.
That was from a previous attempt, and I ended up cutting it off.

- Look in the under-hood fuse box. At the far right corner (as you're standing at the driver's side fender), there's a stud (bolt). That's energized all the time, so be careful.



Move to the left (toward the front of the vehicle) two columns (rows? depends on how you look at it) and note the space between the 7.5A and 10A fuses. That's where the low-profile fuse holder gadget will go. Orientation will be important! Insert the fuse holder such that the wire attached to it is on the right (rearward) side of that fuse receptacle. In this orientation, you'll be able to measure 12V (ish) between that wire and the negative post of the battery. Insert it the other way, and you'll get no volts. This is important.

Be sure to insert the fuse, chosen appropriately for your light. Ohm's Law is your friend here.

The lead from this fuse tap gets attached to the terminal 30 relay (or relay adapter) connection. That's going to be the power source for your light, feeding through to terminal 87 when the relay is energized. That lead, like the stud over in the corner, will be energized all the time, but only allowed to feed your light when the relay is energized.

Reach up in behind the fog lamp and disconnect its harness. You may want to remove the first two screws in the fender liner and pull that material back a little to ease access. Drop the two-connector portion of your new harness down through the available space at the front left corner of the engine box (ahead of the battery), and plug it into the fog lamp and the OE harness.

Now splice the red lead from your new harness to terminal 86 on the relay (or relay adapter), the black lead from your harness to the black lead that runs to your light, and the red lead from your light to terminal 87 on your relay. This completes the circuit to the light, sharing the existing fog lamp's ground connection.

Next, connect terminal 85 of your relay (or relay adapter) to chassis ground. This completes the relay coil circuit.

Take a moment to cut a narrow slot in the fuse box cover to accommodate that red wire's path out of the box, and then put the cover back on.

Ensure your relay is securely mounted, tidy up your wires, and take a break; you've earned it.

After your break, make sure you've not left any tools or materials in the engine box. Don't be like one particular fella I know who left the cover off the fuse box and found it a day later, wedged up against one of the belts. No bueno!

At this point you're ready to test. (Admittedly, we should have tested earlier in this process, but we're fairly confident, right?)

If you can reach both, then put a finger on your relay and twist the knob to turn on your fog lamps. You should feel the relay change state. You should also see your add-on light come on. Success!

If you removed screws from the fender liner, put them back. Now put your tools away, close the hood, and take a moment to enjoy (or show off) your handiwork.