Originally Posted by rabbit73
The DC jack is 5.5mm x 2.5mm (Radio Shack size N)neg.gnd.
By that you seem to be indicating that the collar is negative and the pin is positive on that plug.
Can you pull that plug out of that jack a little to expose the collar while maintaining contact with the jacks wiper and measure low ohms to the chassis for a direct short (Indicating negative ground) with the wal-wart unplugged?
The pin on that jack is easy to tag with a meter probe, but the collar wiper can be a bit tight as you know.
And yes, a regulator is strongly advised for any electronics near any alternator. Somthing simple like the three pin TO-200 cased LM7812
12-Volt regulator chip (Radio Shack Cat# 276-1771) on a small heatsink or aluminum plate. The minimum input voltage across the 78xx series needs to be 2-Volts or 14.0-Volts DC minimum though. My experience with the clones is more like 2.5-Volts, input. So this might work with the alternator online, but not after you turn off the engine.
I'm looking for a 9-Volt CECB to use a 7809 9-Volt regulator IC on. That would work fine on my huge 8D battery bank I already have for my houses 10-KW inverter rack down to 11-Volts or so.
Would work in auto's/camper's too without charger/alternator online.
Or maybe a 5-Volt CECB if there are any worth a bean...
Then there's power outages in house applications.
Three sealed 6-Volt batteries (Available at even walmart for Kids toy cars, etc.) would run this box for a good week. And 18-Volt wal-warts / power-bricks aren't that hard to find for a few dollars on eBay...