Having problems with 1991 350SDL battery going dead if the car is not started weekly.
Having this problem with a new fully charged battery and the old (good?) battery. All cables appear to be clean and tight. The current drain with everything off is 15ma but it jumps to approx. 28 ma. every 1 to 2 sec and back to 15ma. What is normal current drain? Checking with digital meter so I might not be seeing everything. Also had the seatbelt connected light stay on during a trip with belts fastened but it appears ok now.

I don't think I would worry about 28ma. Draws caused by trunk bulbs etc. usually range around 200ma. I would guess that the spec for that car would be 25-50ma.

With a diesel I would try and monitor the glow system. If the system comes on or stays on intermittantly it will keep the battery week. Often a hard onee to catch.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Try disconnecting things such as the glow plug relay. Mine did the same and it turned out to be the power antenna that kept running after turning off the ignition.

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1991 350 SDL
125,000 miles

Most of the 1991 cars have a 2-piece radio, with the tuner in the trunk. The tuner can stay on & draw power. When you disconnect battery to install a-meter the radio will quit drawing it's 400ma. Try hooking up meter w/out losing this info. Or turn radio on w/meter already on(USE 10A scale!!).