WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator - Dual Battery System for RVs, Boats & Trucks - Heavy Duty Black Battery Isolator for Reliable Power Management

No Luck so far making this device operate. I have a 1971 VW Bus and wanted a aux battery for accessories without draining the starter battery. Installation was easy and followed very easily. I have a 7 month old starter battery. Once I hooked in a ground wire from the aux battery to the frame the red blinking light turned solid red as stated in the instructions. I start the vehicle and the blue charging light never came on. Thought, well I will drive around and see what happens. I found out that my starter battery kept draining while the aux batter remained charged...but still no blue light.Basically it has killed my (fairly new) starter battery and I got it replaced - did find out on numerous occasions that the jumpstart feature works GREAT!!!New starter battery in, same thing exactly as written above. Back to square one. Called tech support, "Tim" was very helpful and said it may be that the circuit board is defective and to return it. I did and waiting on a replacement. I hope it works, but the new starter battery has probably suffered some damage from being discharged frequently. Tech support also mentioned that the unit will not work on a positive grounded vehicle and suggested that may be my issue. No, the VW Bus has a negative ground system....but people who may have a European car that has a positive ground system, this will not work.I will update once I get the replacement, but just don't think it is going to work but hoping for the best. The instructions said it goes into charging mode when the starter battery is above 13.4v....well, that is probably the problem as even the starter battery read 12.8 volts BRAND NEW. Not too sure how to get it up to 13.4?Really disappointed this did not work for me so far and caused a lot of troubles along the way. Looks like many people had a good experience.****UPDATE****Batteries, mostly the starter battery was low. Decided to put it on a charger while still in the vehicle. Next morning to my surprise the blue LED light was on! Turns out it is working properly, I was just not getting the proper voltage due to a pre-existing alternator condition. Got the alternator wiring corrected and this product works as described and like a champ!