1990 240 Battery Drain Caused by Short in Fuel Pump Circuit?

Hello and Help!
I have been working on my own 240's for several years and am reasonably competent with mechanics but have little experience with
electrical problems and terminology. I have searched this board thoroughly but have not been able to find the information I am looking for in this particular situation. I have been reading this board for years and don't know where else to turn.
PROBLEM: I have a 1990 240. My battery drained overnight when I recently left the glovebox door open for ~18 hours. The next day I got a jumpstart, drove the car to work, ran some errands in the evening (starting the car several times with no problems), and parked it overnight. The next morning, however, the battery was almost completely drained and the car would not turn over. Both nights the temperature had dipped into the low thirties.
INVESTIGATION:
1) POSSIBLE BAD BATTERY: I took the battery (age unknown) to the local auto parts store and had it charged and load tested, which resulted "good," although I am not sure I entirely trust that considering the battery was almost completely drained twice.
2) POSSIBLE SHORT: I connected a voltmeter/ammeter in series with the negative lead of the battery (now fully charged), which registered current draw of > 150 mA. The car was turned off (naturally) and the radio and interior lights/clock fuses pulled. I don't suspect the alternator, which puts out 14+ volts, but I disconnected it anyway to eliminate the stuck-diode possibility with no resulting drop in the current draw. Leaving the alternator disconnected, I pulled the remaining fuses in the fuse box (corrosion free) one at a time with no resulting drop in current draw. Stumped, I looked under the hood for the problem. When I pulled the 25-amp fuse for the fuel pump circuit, the current draw on the battery went to zero. Eureka! or so I thought.
3) FUEL PUMP CIRCUIT: I checked the fuse and housing for signs of corrosion (non present) as well as the relay under the passenger-side dash (no corrosion present). With the battery connected, I metered between the red lead (#30 at the relay)and a ground and measured current, which doesn't seem right to me. When I completely disconnected the fuse circuit from the battery (disconnecting the wire from the side of the post) and disconnected the relay, leaving the fuse intact, then checked for continuity between the relay lead and ground, the meter shows continuity. At this point, shouldn't I effectively be measuring the continuity of a loose wire with something it is not attached to? It seems to me (and I may be grossly wrong) that there has to be a short somewhere between the fuse and the relay.
QUESTIONS:
The sub-par manuals I have, Chilton and Haynes, have limited schematics and none depicting the fuel pump circuit, so I don't know exactly what I am looking at.
1) Should there be any power drawn by the fuel pump circuit when the car is shut off? I probably would have read about this in other descriptions of battery drain problems and testing procedures.
2) Are there any interuptions/junctions in the circuit between the battery terminal lead and the under dash relay lead besides the 25-amp fuse, or is it a straight shot? I tried to visually follow the harness and don't see any "breaks." I have considered running a bypass wire directly from the blade fuse to the relay in order to see if that makes a difference, but am concerned that I may be bypassing some hidden junction.
3) Is there something obvious that I should be taking into consideration, or am I on the right track?
THANKS: I have almost run out of ideas and am not yet ready to swap the battery and alternator with the hope of correcting the problem "magically." I have to take a trip next weekend and hope to resolve this problem before then. Otherwise, it looks like I will be pulling the battery cable every time I park my not-so-trusty Swedish steed. Any advice or criticisms this group has to offer will be tremendously appreciated. As I mentioned earlier, I only have a passing familiarity with electrics and electrical terminology, so I will be glad to clarify anything in my description that does not make sense.
Thanks Again,
Ezekiel Woods
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To me your method och checking sounds right.
When you did your tests, did you have the ignition key removed?
I am not sure, but I would think the fuel pump is switched via the ignition key. Is there really +12 V at the 25A switch with the ignition key removed?
A good battery has a capacity of about 60 Ah. If it is fully charged it would take 30/0.150 0 hours to drain half the capacity at 150 mA. Even if 150 mA are mysteriously drained, it should definitely not drain a sound battery overnight.
You measured current as "more than 150mA". Was that because your instrument was limited to 150? Could it be several Amperes being drained? That would give you potential problems overnight. Otherwise it sounds as if your battery is bad. Bad batteries typically give full voltage when charged but their storage capacity is close to zero.
18 hours of glove compartment should be no problem. If there is a 5 W bulb there, it draws 0.5 A (rougly). In 18 hrs that amounts to 9 Ah, which would be absolutely no problem for a healthy battery. Even a 10 W bulb for 18 hours should give no starting problems unless you live in Alaska and it's winter.
--
Gunnar

240 Turbo Wagon '84 200 K Miles
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I measured +12 V between the negative terminal and ground cable. With the car turned off and the key removed, I should not detect any current or voltage in that circuit. Right?
Unfortunately, my meter is of the small, cheap variety. When I do the amperage tests the meter pegs beyond 150 mA. I am guessing that it is at least several amperes being drained.
As for the battery, I had it tested at the local parts store, and their equipment indicated my battery was good. Is that sort of bench test reliable? It would probably be a good idea to replace the battery at this point because I don't know its age and it has been drained completely twice remaining uncharged for several days in cold weather. But, I am reluctant to install a new battery, if I have what appears to be a short in the system that will just as likely damage a new battery.
Do you know whether I can directly bypass the suspect wire (buried in the harness) with a wire from the 25A fuse directly to the fuel pump relay, or will I also be bypassing some other component or hidden junction by doing so? I have visually traced the harness and don't see anything that looks like a problem, but since I don't have a wiring diagram for the circuit, I can't be sure.
Thanks, Gunnar, for your input and the brief lesson on amperage, amp hours, and battery drain. As I said, in my initial post, I don't know much about electricity but am trying to approach things deductively. While I am annoyed on the practical level with my current situation in that I need to make a long trip with the car next week, I do appreciate the situation on another level as an opportunity to learn something new.
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"E. Woods" wrote:

Completely draining a battery twice will not necessarily kill it. Also, a battery can test OK under the load a starter requires, yet discharge itself over a period of time due to an internal fault. I had a battery that would start the car fine on a cold day, provided the car had been used recently, but was completely dead within a week if not charged, even when disconnected.

Ordinarily you'd like to see no more than 100 mA draw total with the car off.

The wire goes from the fuse to the relay and fuel computer directly. This wire may be also connected to other things in the fuel system, that don't use current until the computer grounds them. You really need a wire diagram book to know everywhere this wire goes. The fuel computer has memory circuits that need constant power, like the radio. The fuel pump relay only draws current when the fuel computer grounds it. AFTER REMOVING THE FUSE, disconnect the fuel computer from the harness, and see if the draw changes. Do this test with the fuel pump relay, and any other component that is connected to this wire. The only current should be a very small amount (under 10 mA) for the computer memory.

Instead of disconnecting the battery, just pull that 25A fuse.
--
Mike F.
Thornhill (near Toronto), Ont.
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