I'm scratching my head on the same issue right now. Hopefully some of the more experienced folks will chime in.
At the moment, the best idea I can come up with is punching a hole for a conduit fitting on the vertical portion of the body tub that comes out behind the dash. My concern is that it will be an engraved invitation to rust even with edge treatment on the new hole. They make fittings know as "cord clamps" with a rubber liner compressed by an outer nut that should seal well. An alternative would be a 90deg box elbow. That would turn the end down and hopefully make it harder for water to find its way inside.
Whats the best way to run the wiring for light that are mounted on the windshield hinges?
Don't know if there is a best way, but here's how I ran mine. I have flex tubing run from the light, under the light bracket to the windshield hinge. Did it this way to keep the tubing in place and not flopping around from wind, etc. I used wire heat shrink tubes to cover about 10" of the wires as they come out of the flex tubing. Did this to keep the wires together and help hide them. Then I ran the heat shrinked wires behind the hinges and down in the space between the cowling and body and then under the cowling. From there the wires go through the firewall via rubber grommets. The holes I drilled are just above the body/engine ground bolts on the firewall. I connected the ground wires here and ran the hot wires to a relay. I used existing rubber grommets in the lower firewall to enter the cab with wiring to the switch. All switch wires run to relay/battery/ground through the grommet. None are terminated in the cab. The hot wire for the switch is fused and runs to battery.
Late to the party, again. But in case for future times.
Like in dfry's post, remove the upper cowl cover and look close at the upper corners, by the hinges, you'll see there's a channel and a cut out in the panel, just perfect to run the wires through. Almost like Jeep planned for it.
And you don't have to cut holes to run the wires inside, on the left side of the cowl is the grommet that the harness for the wipers runs through. There's your entrance to the dash/inside for your wires to go through.
97 Sahara, 74 Renegade, 72 CJ5, 55 Willy's (the Beast) Boss 302, 6:34 gearing, Bose 901 speakers.
God I miss that Jeep. Forgot the kinda Jeep, 80 SX4.