Fuse box attached to battery causing power drain (pic)

Hey all,

There is a 2.5 amp draw that is killing my battery at night on my 2004 Sprinter 3500. I found the culprit which turns out to be a fuse box attached directly to the positive terminal of my battery. As soon as I removed the fuse box the key off amp draw went to 0. When I reattached it, it had a very light draw but nothing as serious as 2.5a and remained low. Well now it is two days later and after driving the van around for a while, the draw seems to have come back (as my van won't start today).

I have no idea where it goes and what parts it is attached to. It looks like it has some pretty hefty fuses on it (70, 100, 125, 200amp), I also not sure which one specifically is drawing power (will have to investigate further). Can anyone tell me what connects to this fuse box? It looks like an OEM part as there is a Mercedes logo on the back.

Thanks!

That is the "power distribution block" (PDC), featured in many places in the service manual's section 8w (wiring).
Service manuals (look at both 2003 and 2006 for a 2004) are here: http://aie-services-2.net/Sprinter/

Since the PDC serves mainly as a "first fuse" for dozens of sub-circuits (with their own individual fuses), you've only barely started in your hunt. The only thing that doesn't go through it is the starter motor.

My guess is that a relay somewhere is getting stuck "on" (or a dome light is on) and that's the true source of the draw.

This is where a clamp-on DC ammeter is handy: you can sniff each wire coming from the PDC to see where the 2.5 amps shows up.
My (reasonably-priced) favorite: http://www.sears.com/shc/s/p_10153_12605_03482369000P

PDC fuse assignments (page scan courtesy Vic):



--dick

Hey Dick,

Thanks for the response and the links! I'll grab a clamp meter and get hunting!

-Avery

There is another way to do an assessment:
(a) turn off Sprinter (with the 2.5 amp drain still happening)
(b) wait a while (1/2 hour?).. during which time you'll remove the driver's side seat (or at least cushion) and access the relay panel underneath.
(c) feel the individual relays (and the modules on the floor beneath them) ... hopefully one will be warm
(d) that's the culprit.

2.5 amps at 12 volts is 30 watts... that should be easily perceptible.

You could also monitor the current draw as you extract (one at a time) the fuses under the steering wheel and behind the driver's seat pedestal fuse cover.
(note that PDC fuse 6 feeds the under-steering-column fuse box)


--dick

Hey fellas,

So I took off all of the wires and found the drain is coming from the alternator (the first wire with the 200a fuse). Any ideas on how to proceed now? Is my alternator bad?

Thanks,
Avery

The alternator has an internal (attached on the "back") voltage regulator.

It also has a (thin) wire leading to the instrument panel.
Try disconnecting *that* wire from the alternator and see if the 2.5 amp remains.

If so, it's most likely the voltage regulator block (one of the diodes is probably shorted).

Some folks have replaced their regulators (i don't know where the got the part)
Many replace the entire alternator (buy a Bosch, and get one with a new over-running pulley, too)
(the alternator's pulley allows the alternator to "coast" when the engine suddenly drops in speed)

Use the blue-bar search box for "voltage regulator" for others' tales

--dick