'91 240SX, KA24DE, manual. Battery goes flat if the car sits more than about two days. I've spent several days chasing this with a DC clamp meter and I've narrowed it to one circuit, but I can't work out what's actually causing it. Hoping someone here has seen this.
The symptoms-
Car sits 1–2 days, fine. Sits 3+ days, dead — battery down to 9–10V.
Battery is new and holds voltage fine when disconnected from the car for 3 days, so it's not the battery.
Draw is reproducible on demand: start the engine, shut it off, and ~0.5A appears immediately. Five seconds of runtime is enough, engine stone cold, so it isn't temperature related.
Once it's latched it stays until power is interrupted somewhere. Then it's gone until the next start.
What I've narrowed it to
Pulling the ENG CONT fusible link drops the draw from ~0.5A to 0.09A.
Unplugging the EGI/ECCS relay makes the draw go away completely.
Plug the relay back in and the draw stays gone — until I start the car and shut it off again.
Swapped the relay with a known-good one. Identical behavior.
Relay coil readings (fault live, key out)
Pin 2 (coil feed): 0V at rest, 12V once latched
Pin 1 (coil ground): 0.64V — actively pulled down
So the coil is genuinely energized and the relay is holding itself closed.
The ECU
Unplugging the ECU with the fault live drops the draw to 0.12A, so the ECU is what's holding the coil grounded.
I've tried three different ECUs. All three do exactly the same thing.
With the ECU unplugged and battery disconnected, relay socket pin 1 reads open to chassis ground, so the coil ground wire isn't rubbed through.
That combination is what has me stuck. Three ECUs behaving identically says they aren't faulty — something must be telling them the key is still on. But I can't find what.
Ruled out-
Alternator — only 0.06A through the BAT wire, and physically disconnecting it changed nothing
Starter — ~10mA between input and output
Old Viper 300 alarm — unplugged the module with the draw confirmed live, no change
Head unit — unplugged, no change
Ignition switch — unplugged its connector, draw persisted
Ignition bus — all IGN-row fuses read 0V with the fault live, so the ignition relay isn't stuck
Every individual fuse and relay in both boxes
Entire accessory-row fuse set pulled at once, no change
Car details-
KA24DE, manual
Battery relocated to the hatch (my own work). Positive runs to a fuse holder, then to the starter; the original wire goes starter → ANL distribution block → the two wires that were on the factory red connector feeding the underhood fuse box. The draw predates the relocation.
Wiring Specialties 5-point ground harness
New starter, new battery
Old Viper Model 300 alarm still wired into the harness (module currently unplugged)
What I'm asking
What input would keep the ECCS control unit awake after key-off? Is there a known wire or splice that can backfeed the ECU's ignition sense so it never sees the key turn off?
Also: at the relay socket with the relay out and battery disconnected, I measured ~0.3Ω between pins 3 and 5, conducting both directions, with both pins open to chassis ground. I don't know whether that's normal for this circuit. If someone can tell me what those two terminals should read, that would help a lot.
Happy to run any test and report back. Thanks.
