electrical question?

when checking to see if a wire is good, i've been checking for both continuity and resistance. is this good enough or do i need to do anything else? also, a couple of wires are reading ~.005 ohms. is this ok? i have no idea what is acceptable and what isn't.

 

Continuity indication is ok for fast checks to see if something "works or not". It's limitation is that it is still just a resistance check and the threshold at which each meter says go or no-go is different for each meter.

Checking for continuity and resistance is actually checking the same thing only one is giving you a good/bad indicator against an internal reference and the other is giving you a value. To get valid readings you have to make sure your fingers aren't touching the contacts of the meter and that you get good metal to metal contact between the test probe and the object being measured.

Regarding values very low resistances are common in wire circuits. Try putting your meter across a piece of heavy gauge new copper wire and you will be surprised how good a conductor it is. Resistance goes down as wire gets heavier by the way.

High resistance points are usually found at crimped terminals where the dissimilar metals have corroded (usually cadmium, nickel or zinc plate in direct contact with copper). The corrosion occurs between the crimped terminal and the wire so you cannot see it. When it gets bad the corrosion turns into a mini heating element (what electricians call a "hot joint") and usually starts melting the plastic connector housing.

You should check the resistance of each leg from connector to connector, including the crimped terminals, the lower the measured value the better. Anything higher than an ohm or so should be checked out.

 

makes sense. when i would check just the wire i would have .000 ohms, but when i would test plug to plug i would register slight resistance. now that i know what they're called...i got "hot joints" EVERYWHERE. well, not really everywhere but at least three or four connectors are as such.

 

Industrial electricians who work on switchboards find these with an infra red thermometer, hence the name.

Sometimes you can just re-crimp the terminal to restore a good physical contact ... the terminal just bites in a bit harder. Be sure to use the correct type of crimping tool, it has two sides that close to the center. The cheaper more common type of crimp tool just squashes everything and are not suitable for the double crimp automotive type terminals.

If in any doubt replace both halves of the entire connector, you can buy them at most auto parts houses for a couple of dollars each. Apply a tiny smear of dielectric grease to the outside of the terminal, it will help prevent the air and moisture getting to it and corroding it again.

Be sure to maintain the correct color coding/terminal orientation and wire configuration or the next time you have a problem you'll be tearing your hair out

 

If limited to continuity or resistance checks, go with the continuity test as most meters use more current for that test so it is more likely to find a fault.

Comment based on results of testing 4 multimeters only.

 

testing from end to end is only part of it, if your in a plug make sure that you only have continuity to the wire your testing and then check for continuity to ground.
a 82 750 maxim is the only one i really got into, but there were mistakes in the factory book

 

Most meters are going to get squirrely at very low resistances - below 1/4 Ohm or so. At that point, a lot of what you're measuring is the resistance of the test leads themselves, and the resistances at the points where the probes touch the circuit under test. You should start by crossing the probes, letting the meter settle, and using the resultant value as known "zero". For instance, if crossing the probes gives a value of .15 Ohm, then a reading on a circuit of .45 Ohm really means .3 Ohm resistance in the circuit itself.

If you find you're getting lower readings from circuits than you do with the probes crossed, this may be an indication that their is voltage present in the circuit and that's affect (maybe drastically) your readings.

How low is "good" depends a bit on the purpose of the circuit. In general, as Ian said, below an Ohm is probably OK. Exceptions to this are high current circuits like the battery ground strap, or the starter wire. These are meant to carry dozens of Amps, so they need to have much lower than one Ohm resistance. Turn signals, the alternator, tail lights, and the head light are other examples of high current circuits on the bike.

Is this a general question, though, or are you trying to solve a specific problem?

 

i'm basically trying to understand this bike's electrical system, wiring diagrams, etc. i'm new to this so i'm learning...slowly. i've put the valves in spec, rebuilt the carbs, and a whole bunch of other mechanical stuff and now it's time for the wiring. prior to taking the bike apart, i was occasionally blowing the fuse to the headlight, when i replaced the fuse, it would work temporarily only to blow again. usually took a couple weeks of daily riding to blow one. i also have "hot joints" at the ignition connector plug (behind headlight), the regulator rectifier (it gets HOT), and on the headlight connector plug. although i do have melted plugs...these wires are still showing no resistance and have continuity. thanks everyone. thanks everyone

 

Thanks SQLguy, you made a really important point. You need to understand what the meter is telling you.

If the circuit is showing very low resistance and "continuity" is ok then the circuit is indicating OK .. so move on to other problems ... that's the best outcome. "Hot joints" can go away just by jiggling a connector or going over a speed bump (welcome to the world of auto electrics). If the problem persists keep looking.

Good luck.

 

That regulator/rectifier plug is a problem one. It's pins tend to oxidize and build up resistance. Then, as you've seen, they get hot, and start melting the plastic, and get oxidized worse, until they eventually lose contact and you're alternator stops charging so well.

If the connector's not too far gone, you can clean up the pins with a wire brush, load up the connector with some dielectric grease, and keep using it. If it's pretty melted, though, you should cut off the old connectors and solder in some new ones. Don't know whether Chacal has a suitable connector set, but, if not, you can probably pull the regulator and bring it to NAPA to see what they have in a similar layout plug/socket pair.

Bad connections in the regulator plug could also be leading to overvoltage on the system, which might explain your intermittent headlight fuse blowing issue.