Generator cutout converted to diode

[Dave39MD]

To start I am electrically challenged. 

 

Testing my new wire harness I started with the battery to amp meter and found it was grounded. Under the dash I traced it to the wire coming from the cutout. With the bat wire off the cutout nothing is grounded on the positive side. On the 20k scale the ohm meter reads 7.25 with the cutout connected.

Since I don't really understand the diode conversion is this normal and no worries or do I have a bad converted cutout? 

 

Thanks

 

Dave

 

[Bloo]

I'll say up front I don't like these, but others rave about how good they are. Your mileage may vary.

 

The diode should connect from one post to the other, and nothing to ground.

 

It does matter which post is which, and if the cutout were intended for a positive ground car, the posts might be marked backwards for a negative ground Chevrolet.

 

To test the diode, use the diode check function on your mutlimeter if it has one. It probably does. Look for the diode symbol. Connect each multimeter lead to each cutout terminal and read the meter (it reads in volts). Then reverse the leads and read again. It should read about 0.6V or 0.7V one way, and OL or open circuit (no connection) the other way.

 

There should be no continuity from either post to the case (ground).

 

Another method: Take a car battery and an old incandescent test light. Connect the test light lead to the first battery post.

 

Touch one cutout terminal to the second battery post. Then touch the test light tip to the remaining cutout terminal. Then reverse the cutout terminals and try again. The light should light brightly one way and not at all the other.

 

Similarly to check for shorts to ground, connect the test light lead to the first battery post. Connect the cutout case to the second battery post. Touch the tip of the test light to each cutout terminal. It should not light on either one.

 

These tests are ONLY for cutouts that have been gutted and have an alternator diode soldered inside. They will not work for electromechanical cutouts.

 

Have fun!

 

 

Edited February 2, 2022 by Bloo (see edit history)

[Dave39MD]

Thanks Bloo. I had heard good things about these and it was on the generator but I like the original Delco-Remy unit better.

 

Going back to try your tests, here is a photo of the cutout.

 

Dave

[hook]

In case you need new of either kind, go to www.brillman.com they have them and a lot of other electrical stuff.

[Dave39MD]

Thanks Hook.

 

Bloo, No ground on either terminal. I did the diode test and it was .610 on one meter and .521 on another. When the leads were reversed, 0.

 

So I went back and tested for the positive grounding problem and nothing showed up when everything was connected as it was. Could the testing of the diode have changed anything?

 

thanks

 

Dave

[Bloo]

It sounds to me like it's good. I don't think you could change anything by testing it. I'm not sure an ohmmeter test is useful in this case.

 

When it is back together you can check at the battery by disconnecting a battery cable and connecting an old incandescent test light between the post and the cable you disconnected from it (in series). If it glows bright there could be a problem.

 

After checking and verifying that the light does not glow bright, you can take a multimeter set to amps and connect it in series like the test light was. That probably involves plugging at least one multimeter lead into a different hole as well as setting the dial. Don't forget to put the multimeter lead back in the other "normal" hole afterward! Ammeters are a dead short, and you wouldn't want to get surprised by that trying to test voltage on something later. Things would melt.

 

I wouldn't get too upset at 0.050 Amps (50 mA). Most modern cars draw more than that, but I would expect a LOT less here if it is only the generator and cutout responsible and nothing else. If you have 0.500 Amps (500 mA) that is definitely a problem. Nothing draws that much normally except emergency vehicles, and they have a lot of dead batteries.

 

If you have an electric clock disconnect it before doing any of these tests. It will fool you, and do so intermittently.

 

Edited February 2, 2022 by Bloo (see edit history)

[Dave39MD]

I think you are telling me I should not use an ohm meter to test for shorts, I thought it was an improvement over my past method watching to see what catches fire! 

 

I will put a battery in and use an amp meter to see how it goes.

 

Thanks

 

Dave

[Bloo]

Well, in THEORY there is nothing wrong with an ohmmeter. In practice, on cars, you will chase your tail. The test with the test light will prevent burning anything up. If the light burns brightly when in series with a battery cable/post, something is wrong and you need to go after that first. A dim light or no light means it's ok to proceed with the ammeter.

[Dave39MD]

will do, thanks again

[jdome]

You can easily & safely test a diode with an ohm meter or multimeter on the proper ohm scale.  You test the "front-to-back ratio" by connecting a test lead on each end of the diode, then reverse the leads. The meter should read low resistance (or continuity if you prefer that term) in one direction and hi resistance (may read open) in the other direction. you have to set the meter to a low scale setting. For practical purposes the resistive values don't matter as long as there is an obvious, readable difference; as opposed to either open or shorted (0 ohms) in both directions. This is a safer way to test the diode or anything else, than using a battery and light method due to the fact that a battery can supply almost unlimited current until it burns something up if you happen to short it out. In reality, an ohm meter is a battery & light tester that gives a useful measure of "brightness."  It has its own built in battery that it uses to supply small limited current thru the component or circuit you are testing and calculates the current as resistance. As long as you do not have any other battery connected to the circuit, there is no danger of damaging the circuit, parts or meter.  Good meters, either analog or digital have some limited type of over-voltage or over-current protection but don't tempt fate. If you have a meter that no longer works in the ohms mode, open it up and check the fuse (if it has one) and check its internal battery. The battery is typically a couple 1.5v cells or a 9v snap-in.  OR the meter is foobared. 

 

Never test anything in the ohms mode with the car's battery hooked up. Disconnect the non-grounded post and make sure it is insulated from chassis ground, - it won't damage anything but if you are testing continuity  in the harness, you might read a false path thru the unintended ground.

Never put a meter in series with the battery, in any mode, unless you are certain how to properly use it to measure current (amps).  

The only thing you can do safely measure with the battery hooked up is measure voltage in the volt mode. 

 

The ohm meter is your friend. 

[jdome]

Don't use an ohm meter to check for "shorts," use it to check for resistance (continuity) from some known point to ground.  The car battery has to be disconnected.  Zero ohms is a dead short. Almost anything analog on an old car like a bulb or gauge will be less than 10 ohms.  Radios, electronics, LEDs or anything digital can read hi or low resistance. Take a loose taillight bulb and measure across the filament contacts and it will typically measure 2 or 3 ohms on the RX1 scale, but it will appear as a "short" or produce the "continuity test beep" on the RX10000 scale, because it can't measure the small difference between 0 and 2 ohms on the high scale; so the filament appears as a wire shorted across the meter. If you can isolate the tail light wire from the headlight switch and test resistance between that line and ground, and you read 0 ohms on the low scale you have a short somewhere on that circuit. If you have no reading you have an open circuit somewhere (could be a bad bulb or corroded socket.) You should see 2 ohms thru the bulb to ground except 2 tail lights in parallel will cut the resistance in half.  You could measure the tail lights wired to the switch contact with switch off but you will also measure the head and dash lights in parallel as well, which will cut the resistance to less than half ( it is not linear division). You should be able to measure a fraction of an ohm from multiple bulbs in parallel on the Rx1 scale.  The point is, you should be able to isolate circuits and determine open, zero ohm short, or a desired resistance.

[Dave39MD]

jdome, Thanks for the info I will give the tests a try. 

 

No vehicle battery is in circuit at this point I am just checking my wiring harness and my work.

 

Dave

[Dave39MD]

I checked it all again with the ohm meter, a test light and the amp meter and it was good to go. The lights work, starter turns, everything seems to be working except the clock. 

 

Thanks again for all the help.

 

Dave

[TerryB]

1 minute ago, Dave39MD said:

I checked it all again with the ohm meter, a test light and the amp meter and it was good to go. The lights work, starter turns, everything seems to be working except the clock. 

 

Thanks again for all the help.

 

Dave

Do clocks EVER work for more than a day😀.

[Dave39MD]

Well no but at least it is set to 5 after 5.

 

Dave

[hook]

13 hours ago, Dave39MD said:

I checked it all again with the ohm meter, a test light and the amp meter and it was good to go. The lights work, starter turns, everything seems to be working except the clock. 

 

Thanks again for all the help.

 

Dave

At least your clock is dead accurate twice a day! 

[37_Roadmaster_C]

Beat me to it by one correct time read......