engine and drivetrain obtaining complete wiring for 74 BMW at wits end

[vintage_car]

Well my happy days have come and gone. Had alost 2 weeks of joy, but the electric gremlins in my car hae about killed me. I have not been wanting to rip out all the old wiring and start over, but I'm afraid this is what has to happen. I have no idea how it is happening but after about 4 days of sitting, the car won;t start...again! replace battery, altenator, and voltage regulator, nothing has fixed this slow drain of power. I drove the car almost 200 miles, but it has rained the last few days so I kept in covered. Tried to start it last night and it had juice enough to turn the engine over one time and then just tick. Not sure where this electrical drain is happening and I'm at wits end about it. Where does one aquire a full wiring setup for a 74 2002? I need from headlight to taillight and everything in between.

[winstontj]

The wires from the rear bumper up to the front of the driver's seat can be checked very easily and certanly without a wire diagram. The wires are all bundled together and run up the driver's side of the car. Pull out the back seats and lift up the driver's side of the carpet. You'll see the braid and just check it/follow it all the way to the back. Its' really simple.

If I had to bet I'd say that something under the dash (VERY SIMPLE) or under the fuse box is giving you your problem. Have you lifted up your fuse box and checked for any melting/wire issues? How about looking under the dash for any old hack-looking sterio installs? Anything else under there look like a rats nest of wires?

Are you sure that your battery isn't dead and won't hold a charge?

[c.d.iesel]

replace your alternator with one from a reliable source

(BMW) - - -you got bad diodes

[vintage_car]

when I put a light tester clamped onto ground and I touch the fuse on #1 and #2 it lights up, is this a problem, or are those 2 fuses supposed to have power with the car off? there is an aftermarket stereo that has been in there since I've owned it. I can remove it for the time being to see if that helps. What are good wires for ground, power and memory to splice an aftermarket stereo to? The battery charges and shows good, but I may see if they will swap me with another one off the shelf. the altenator is brand new, got it last week along with the voltage regulator.

[DavidLMM]

Get a good wiring diagram. I have a nice color laminated one from Prospero. JFGI "prospero wiring diagram". Note that there is a difference for 1974-up models.

Can you load test your battery? If so, do that, see what your sitting voltage is. Just because a DMM says a battery is "good" doesn't mean it really has any power. Any Auto Zone, etc. type place can load test it for you, but I don't know that I'd trust them 100% since they like to sell batteries.

If that's OK, start the car, see what your alternator is putting out - should be 13.8v or so. Make sure your wiring is in good shape - alt. properly grounded, other grounds in good shape, etc. If the battery tests good, and your voltage regulator is allowing your alt. to put out the right voltage, it's something else - dome light, radio, alarm, etc.

As someone else mentioned, look under your fusebox for possible shorted areas. If everything else checks out, start looking for current drains. Identify which circuits are supposed to be hot, verify. ID circuits that are _not_ supposed to be hot. If you find any that are, start tracking down those components. It's a 2002, not a 760, there really isn't that much to our electrical systems. On my E30 M3, I had a similar problem. Went thru the process of pulling a different fuse every night until I found the problem - a bad external mirror heater - hard to diagnose, impossible to see or even feel unless it is cold enpough to see it _not_ working.

Do you still have my e-mail address at work? Let me know how you make out.

David In Nashville

[us4736]

somthing is draining the battery when its just sitting so you have too put and ohm meter on and see how much its drawing .then start pulling fuses and see if it goes down if not it could be a diode in the alt so unhook the alt and see if it changes on the ohm meter . wiring can be a big PITA but its just prosess of elimination

[Mike Self]

they power such things as the 4 way flashers and ciggy lighter.

You've got a power drain somewhere....have you tried (with a charged battery) removing the fuses one by one? Let it sit and when the battery stops draining, you've found the circuit with the problem. Then you only have to troubleshoot that single circuit.

mike