NEED HELP Pulsing battery drain???

fixit

New Member
2004 Chevy Silverado 3500, Extended Cab, Long Bed, LLY Diesel, Dual Battery, 6 Way Electric, Heated Seats:

I have a problem that I have never encountered before. After driving my truck from Austin to San Antonio to have a Maxon liftgate installed, I returned to Austin two days later and parked the truck. At this point, everything seemed fine. Unfortunately, for the next two it rained and the truck stayed parked. On the third day, I was going to get busy, but when I punched the key fob, nothing happened. I put a digital Voltmeter on one of the batteries and read 1.9 Volts! So much for $500 worth of six month old, AGM Batteries. I put the best charge that I could on the batteries using a power supply and then started the engine. The alternator put out 14.7 Volts for a couple of minutes and then began to taper off the charging, (normal behavior). From this I took that the alternator was not the problem. Next, I made a test connector out of a "J Case" fuse and connected a 20 Amp current shunt and meter to it. With the truck's key off and removed, driver's door open and all visible accessories off, I began swapping out the "J Case" fuses one at a time. The LBEC 1 and LBEC 2 buses showed only a few milliAmps of battery drain, but the MBEC(1) bus indicated something strange. This bus exhibited an approximately 6.5 Amp current pulse lasting about one second and repeating every six seconds.
As far as I can discern, the only things that are served on this bus are the electric seats and the door modules. Unfortunately, tracking the wiring beyond the fuse box becomes more difficult, especially if you are an elderly gimp, so I am hoping that someone has seen this symptom before and can save me some effort. I don't know if I can still hang upside down under a dashboard, or not. So, does anyone know what can cause this pulsed battery drain?

fixit - I ran, screaming form the grease pit.
 

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