I tried to identify this location when I first went through the episodes for this thread. It's the scrapyard from the end of 'Uncle Boss' in season 3. The 'Hogg's Auto Wrecking' sign seems to have been added next to the original sign. I say this because the part of the sign on the right that's readable appears to say 'VW & Compact American ...' and they wouldn't have made a sign with 'VW' named on it.
After re-reading this thread I spotted MaryAnne's post with the pictures of Robert Culp (does she have any other kind) outside the San Fernando Valley Generating Station with the cars piled up in the foreground. This, coupled with Mufn's comment that 'there are like 40 bazillion junkyards, scrap metal recycling, and car wrecking yards around there' made me revisit the area. The picture below was the clincher as it shows the run-off from the Hansen Dam at the top of the picture with the Hansen Dam Golf Course to the left. The waterway below the dam passes the scrapyard on the left, and there are no roads between here and the dam, so we must be on Glenoaks Boulevard, just north of Truesdale Street. You can see for yourself on Google Maps.
Both the scrapyards and Sheldon Quarry behind have changed considerably since filming. To help visualize them as they were then I've included aerial views from 1982. I've highlighted the dam at the top and and the two scrapyards at the bottom. If you've looked at the Google Maps link above you'll notice how much smaller the quarry is here. The 'L' shaped building at the bottom in the center is still standing, but the left scrapyard is now offices and the one on the right is occupied by a couple of car parts businesses; one selling Japanese parts, the other specializing in foreign cars.