I was just thinking about something like this a couple days ago. Would have been great to work out if it was the brushes or the regulator that was going. Awesome find guys.

*where’s the thumbs up emote…ha!*

OT… “Too bad this doesn’t give me any solution for finding a short which keeps burning out the fuse for the stop light in my wife’s Mazda 323.”

Check any flexible leads attached to the trunk / hatchback… where they bend is a common failure point for that kind of problem.

@Sam

You could just abandon the horn and brake light circuits and run new wire. That may be faster than finding the short.

@Ardu
You won’t have to follow anything — your car will probably be engulfed in flames shortly. Easy!

Thanks for all the suggestions, who knew we had a few car wiring geeks roaming Hackaday?

The whole problem has been frustrated by the fact that a rodent (probably a mouse) decided to make a nest in the engine and chewed up some of wiring to drag into its nest. I’ve had to clip and replace sections of chewed wires and everything seems in proper order. Disconnecting the bulkheads where I did the replacements didn’t help locate the short, however, so it’s elsewhere. On the other hand, running so much wiring has allowed me to find severed wires all over and I’ve got every light functioning in the head and tail lamp assemblies… except the stop light and horn.

Agent420, I’ll definitely try looking there. I’ve read that other common places are where bundles go through holes cut in metal (they come loose from their retaining wires and chafe). It makes practical sense to expect them there.

Jc, it’s definitely a resistive short. The fuse blows immediately when the stop light circuit is completed (pressing the brake). I’ve been using a continuity tester and disconnecting sections of the harness from one another (basically I ground one terminal of the multimeter and connect the other to the hot lead – the battery is disconnected of course). I almost wish that the wiring was broken up into shorter sections which could be disconnected, that would sure make this process a lot easier (and cheaper to just buy a new section of the wire harness instead of repairing broken ones).

Na, yeah, I’ve considered that and if it comes down to it that is exactly what I’ll do. It’s something I’d hate to do to the next owner of the vehicle, should we choose to sell it later on.

Ardu, I’ll pass on that. ;) The last thing I need is to fry a section of the harness when almost everything is functioning save the fuel gauge (on another circuit and it’s never worked) and the tail/horn assembly. This vehicle is a 1988 Mazda 323 turbo (there weren’t very many ever made) so finding a replacement harness wouldn’t be a fun task.

Nice project — I’ve been thinking about doing something like this for a while, and this looks a lot more elegant than a current transformer would be.

@jc
Most modern transmissions also have shift solenoids that direct transmission fluid through the appropriate channels, allowing the transmission to be more precisely controlled by a computer. I don’t have any idea what kind of current they draw, but I would imagine they’re in the same ballpark as the TCC solenoid. A 4-speed transmission has 2 shift solenoids, and I guess that 5 and 6-speed transmissions have 3 (but don’t know for sure.)

That’s not how you hook up an ammeter. This will only indicate what the alternator is sending out. It does not provide the full picture – for example, current draw with the motor off, as it can only read what the alternator is producing. An automotive ammeter is properly connected to read all of the current in all systems except for what flows in the large cable between the battery and the starter. That is different than can be measured by the subject device.

The picture shows his problem, he is using a re-manufactured alternator.

@OTLabs:

You may want to take a look at this part sold at Digikey. Looks like what you are looking for.

http://media.digikey.com/pdf/Data%20Sheets/LEM%20USA%20PDFs/lts25-np,e.pdf

JGN, “what the alternator is sending out” is what the truck is using, which was the point: the truck runs off of the alternator. The truck doesn’t run off of the batteries. The batteries are only to start the truck, and then the alternator charges them back up. You can actually remove the batteries on some vehicles while the engine is running.
Since the alternator and batteries are bonded, if you wanted to measure battery draw just move my device to the battery.
This sensor is actually better than an automotive ammeter, because it uses the hall effect to measure current. There is no current sense resistor, hence no voltage drop or power loss. And unlike a current transformer, the hall effect device can measure DC.

Eraser, I don’t believe a clamp-on fluke will measure the DC current from the alternator…

Alright, but it does not graph the output like this guy did for only a fraction of the price. That fluke costs $300+.

“That fluke costs $300+.”

Aren’t “Fluke” and “$300+” redundant…? :-|