FFUUU- Battery being drained by Stop Light circuit

[Rope-Pusher]

Soylent Green is people!

That movie was nowhere near good enough for the notoriety it has gained.

Shut your mough - it starred Moses in the role of Charlton Heston. Don't get any better than that.

It has famous quotes like:

"Pharoh! I'll give you the Rod of God when you take it from my cold, dead hands!"

and

"Manna is people! We've got to stop them somehow!"

[IMBoring25]

Damn you electric educated folks...how are you getting 16.7 ohms out of anything I posted? There's something here for me to learn.

Voltage (V or E, Electromotive Force, in Volts) = Current (I, in Amps) X Resistance (R, in Ohms)

Solve for R --> R = V/I. For a 12 Volt source dissipated to ground (This should be what's going on) at 0.72 A, R = 12 / .72 = 16 2/3 Ohms.

You can also use P = IE to conclude that 8.64 W are being dissipated when the battery is charged to 12 V.

As for the shift interlock, that's handled by a solenoid at the shifter inside the vehicle. I had to take apart the entire console area to reach it.

A solenoid is a fairly typical way to actuate the locking-in or locking-out of gears, but it does have to be in a circuit that renders it "sentient" of whether the conditions for the gear to be locked in/out are met or not.

[Rope-Pusher]

Damn you electric educated folks...how are you getting 16.7 ohms out of anything I posted? There's something here for me to learn.

Voltage (V or E, Electromotive Force, in Volts) = Current (I, in Amps) X Resistance (R, in Ohms)

Solve for R --> R = V/I. For a 12 Volt source dissipated to ground (This should be what's going on) at 0.72 A, R = 12 / .72 = 16 2/3 Ohms.

You can also use P = IE to conclude that 8.64 W are being dissipated when the battery is charged to 12 V.

As for the shift interlock, that's handled by a solenoid at the shifter inside the vehicle. I had to take apart the entire console area to reach it.

A solenoid is a fairly typical way to actuate the locking-in or locking-out of gears, but it does have to be in a circuit that renders it "sentient" of whether the conditions for the gear to be locked in/out are met or not.

Oh, so you bought into that myth of the "12 Volt Electrical System"?

[watkins]

Its 12.6, thank you very much. More if the alternator is dandy

[Rope-Pusher]

Its 12.6, thank you very much. More if the alternator is dandy

13.2 right after coming off of a charger, but that fades quickly. My point was that calculating ohm from the current assumes you knew the voltage, which, like your mileage, may vary. Same goes for engines on a dyno - dyno measures torque most directly, then calculates horsepressure based off torque at an rpm. Each measured term has some error associated with it. More terms in the calculation = more error in the derived data. Plotting torque curve is therefore more accurate than horsepressure curve.

[IMBoring25]

I'm well aware a well-charged battery exceeds 12 volts. It was what I'd call a Reasonable Order of Magnitude estimate that suggests the circuit that's not supposed to be there probably isn't running through another accessory.

[theholycow]

Damnit. Of course the wiring isn't as simple as the diagrams make it look. I wasn't expecting anything better (in theory, theory and practice are the same...but in practice they differ).

I worked on it for over two hours this morning but I give up. I can't follow the wires, I can't find anything that looks worn or broken, I can't figure this out. Stupid thing.

[Rope-Pusher]

^ and the Scotsman said "Nothin's worn under me kilt. It's all in perfect workin' order".

So, what happens if you take electrons into your own bare hands and run a new power lead, thru a fuse, to the brake light switch?

[theholycow]

I was considering doing that. I think if I did a hack, though, it would be a relay that activates that circuit using the brake switch as a trigger and entirely disconnects the circuit when at rest...or maybe rewire the circuit to go through the switch first or something.

You know what's stopping me? Eventually this thing will end up at my father in law's garage for some kind of repair, and the guys there will bust my balls about the hack.

[IMBoring25]

A temporary hack would at least confirm the diagnosis, however. Then you could decide how much trouble you wanted to go to to do it right.

[theholycow]

I think the diagnosis is accurate. I pull that one fuse, the drain stops. The hacks all involve leaving the fuse out permanently or automatically disconnecting it so there's nothing more to learn from it than just having the wife pull the fuse when she parks.

[Rope-Pusher]

A temporary hack would at least confirm the diagnosis, however. Then you could decide how much trouble you wanted to go to hack it right.

Hide the wire in a fake nitrous line. Secure the energy drink bottle on the center console and wire in a switch that "ARMS" you brake light circuit. FIL will NOT be disappoint! (is he likely to try it out?)

[IMBoring25]

Its 12.6, thank you very much. More if the alternator is dandy

My scangauge gives me 13.6-13.7 after a cold star, and it settles down t o around 13.2-13.4 after a while. If it's at night with my headlights on, it is 13.5-13.6. If I am on the highway (high RPMs) I will hit 13.8 usually.

I have not used my multimeter to make sure. so much for the "12v" system.

I suspect he wasn't checking for an overnight battery drain with the engine running. Engine running is a completely different matter, when voltage is coming from the alternator, not just the battery. Some of the excess is used, among other things, to charge the battery.

A fully-charged battery will tend to measure around 12.7V. 13.5-13.6 actually sounds on the weak side for when the alternator's spinning. Most automotive systems I've dealt with have no problem hitting 14 or more with the engine running.

It's not uncommon for batteries to test higher than they are rated. Alkaline AAs, AAAs, Cs, and Ds are nominally 1.5V but will typically test closer to 1.6 when in a high state of charge.

[IMBoring25]

Try shifting out of park with the fuse out. If she forgot to take the fuse out and the battery flattened, that would be bad enough. If she forgot to put the fuse IN, you definitely want her to have not being able to shift out of Park as a reminder, since the alternative is driving around with no brake lights and a cruise control that won't disengage with the brake pedal, not to mention that I'm not sure what the ABS system would make of the incorrect input.

[Rope-Pusher]

It's also common to run higher alternator voltage after a cold start - to charge at a higher rate. After battery warms or after a time interval, voltage regulator cuts back the voltage to avoid overcharging / overheating the battery.