I'm having a bit of a head-scratcher with a parasitic drain on my relatively new-to-me '99 S70 T5M, and I'm hoping you might have some insights or suggestions on what to try next.
What I’ve Observed & Done So Far:
- Parasitic Drain:
- The car is drawing about 132–148 mA when off.
- I disconnected all fuses and relays (even some hidden ones under the cover next to the fuses), but the drain didn’t drop.
- Aftermarket Modifications:
- The car had an aftermarket subwoofer connected directly to the battery—I've since removed it.
- There's also a modified aftermarket ECU, which I pulled out of its socket, yet the current draw remained the same.
- Voltage Measurements:
- Battery Terminals: Measuring across the battery (with the negative cable connected and positive cable disconnected) shows 12.81V.
- Fuse Box Circuit: Measuring from the positive battery terminal to the bundle (four wires) going to the fuse box gives about 12.80V—this branch appears solid.
- Starter/Alternator Circuit: However, measuring from the positive terminal to the wire that goes to the starter (and then to the alternator’s B+ terminal) reads 11.68V, which is roughly a 1.13V drop.
The voltage drop on the starter/alternator branch suggests there’s extra resistance or a load in that circuit that's causing the parasitic drain. I’m wondering what could be drawing power on that specific circuit when the car is off. Could it be a failing alternator (maybe a bad diode in the rectifier), a loose or corroded connection, or something else? I was able to get a meter on the B+ terminal directly, but having some trouble disconnecting things to get a proper test on it.
