There's more than one place to put it, but I just T-ed into the line that goes from the overboost protection relay to the ALDA. (I can shoot a picture of this is you want). I then ran the line through the firewall behind the instrument cluster. I had to pull the cluster, but that was a good time to change the bulbs in it. I then ran the line behind the climate control, past the radio and out into the ashtray area. The lighting was real easy there because there are already wires right there for the light in the ashtray (two + and one ground) I just put crimp-on connectors and plugged it right in. The charger I bought from the dealership because the one I pulled out didn't seem to work (but the connections checked out OK). The black circle around it is just a rubber washer I cut to use as a gasket (there's one on the back, too) to hold the charger in place.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)