Testing Wiper Switch Continuity

[charliec]

I'm trying to test the wiper switch for the '68 Dart variable speed wiper motor. Pictured are the instrucstions from the shop manual. As I understand "continuity", a "0" reading on the ohmmeter indicates no continuity, i.e. no connection between the two points. A positive reading of any magnitude on the ohmmeter would indicate that a connection over which a current could flow exists between the two points.

If the above stipulation is correct, is the chart from the manual telling me that with the switch in the various positions, i.e. "off", "low", "high", the probe between the named points should read "0"? Likewise, if I get a positive resitance of any magnitude between any of the designated points, it would indicate a bad switch for that position?

 

[Dana67Dart]

As I understand "continuity", a "0" reading on the ohmmeter indicates no continuity, i.e. no connection between the two points

0 ohms is perfect continuity, meaning there is no resistance to the flow of electrons


1,000 ohms is a lot of resistance, but many electrons will flow through it.


1,000,000 is so much resistance there is almost no electrons passing through it.



"OL" (so much resistance the meter can not display it) is the typical indicator of an open connection no connection from one point to the other, no electrons will moving from one point to another.



Think of it like this.

If the ohm meter leads are not touching what does the meter read.

If you touch the leads together what does the meter read.


A reading of 0 to 0.5 ohms is basically good continuity or connection.


1 to 5 ohms is a bad connection and needing to be resolved.

Looking at the instructions in the FSM it looks like the test is looking for as close to 0 ohms as possible between

B and B/U
B/U and P
etc.
In the switches respective positions


The difference is that between
A and F1 the resistance should be variable as the lever is moved.

"P - Open" is odd as it is not being checked between another point.

 

[charliec]

So, if I understand you, when I go through all of the points in the FSM table, I should see between 0.0 and 0.5 ohms at each one if the switch is good.

 

[Dana67Dart]

I believe so.

The best way to tell the value on your meter you should be looking for is touch the leads together.

Let's say it reads 0.1 ohm and if the switch reads 0.1 ohm it has a good connection. (For the purposes of this test,)

 

[67Dart273]

You have a lot to learn and I'm not trying to be mean.

1...Lower reading AKA lower numbers in the ohms/ resistance function, means that current flows better, or "better" continuity
2...Different meters have different displays when "open" or "infinity." Consult the destruction manual. Sometimes it's INF etc, sometimes a dashed line, etc

3...Never use a meter in the "auto range" function when checking for low resistance. Always set the meter manually on the lowest resistance scale, and this varies meter to meter. ALWAYS short the leads HARD to get the low reading. I will often be .3--.4 ohms, showing the resistance in the test leads and connections. So anything you measure will be that or higher

4...The lower the resistance, the LESS accurate an ohm meter is. Older analog meters were not very useful below about .5 ohms and sometimes below 1 or 2 ohms.
5...NEVER trust ohm readings on something like a switch. Switch contacts can move or make better/ worse contact from slight movement or vibration

Ohms/ resistance readings really often don't tell you much. This is because a contact can sometimes show low resistance if it happens to "make" but a poor contact UNDER LOAD can act up.

++++++++++++++++++++++

Generally it is much better to check switches and other devices with VOLTAGE rather than resistance and check them UNDER LOAD with voltage readings to look for high resistance problems

Example, in the case of say, a fog light switch. There are different ways to approach this. ALWAYS attempt to get into your mind the full functional path of a circuit so you can visualize what might be going on

In the case of a simple fog light circuit, you might have
A....Junction point for power tap off fuse panel, whatever
B....Inline fuse holder..........wiring......to
C....Switch and the wire crimp ends at the switch
D...wire routing out to the fog light mounting area, a branch splice to route power over to the other side, and of course connection to the lamps

"Let's say" they seem dim. How do you "chase" that?

One way is to (if necessary) extend one test lead so you can clip a good solid ground to the battery for the meter. Now with the lights powered on, "chase" the voltage drop.

1...Measure and note battery voltage right at the battery post. Measure voltage at the tap off point. Is it lower? Note that and how much
2...Check the downstream side of the fuse. Often this takes thinking and imagination. Sometimes a scrap strand of wire jammed into the holder so you can access it.

3....Now measure both sides of the switch. is the power side higher than the output to the lamps? VOLTAGE DROP in the switch, note this and how much

4...Now move down to the lamps. Is the power right at the lamps connection any lower than at the switch?

5..DON'T FORGET THE ground side. Now clip your meter to the ground battery clamp Measure the voltage at the ground wire connection right at the lamp. Do you read anything? How much? Perfect is zero

You have just chased the path of the circuit all the way from the ground point back through the circuit to the battery. You should have a good idea of where voltage is being dropped in that circuit.

 

[Mike69cuda]

Del makes a really good point. Ohmmeters are great liars On low resistances. It is easily demonstrated with a simple experiment you can do at home.

Get a few feet of stranded hook up wire.
Strip both ends, but strip one end back a few inches where you can “birdcage“ the strands.
Hook your ohmmeter up to both ends so you get a short.
Start cutting strands one at a time and watch the meter.
You will notice that the meter reading does not change hardly at all till you start cutting the last few strands.

So, using an ohmmeter to measure a low resistance like a wire (or a switch), you often can’t tell whether you have a good connection or a bad connection. It only tells you that you have ”some” connection.

As many others have said, I like using a taillight bulb and a battery charger (or an old 12v wall cube) to troubleshoot with. ***Don’t use a car battery or something with a lot of power in case you short something***. I grew up a poor boy, so we didn‘t have meters, all we had was light bulbs, haha.

 

[Dana67Dart]

I should see between 0.0 and 0.5 ohms at each one if the switch is good

The problem with ohm meters is that they don't tell the whole story.

When there is a load ( motor, light, etc.)
The contact can be bad.

Without a load it might read good.

To do a more indepth test you would need to place a load across the contacts and measure voltage drop.

IMHO

If the contacts ohm out ok you are probably good to go.


If you have been having issues with the switch then a load test would be in order.

 

[charliec]

Very helpful, guys. I will piece it all together. Thanks for the input.

 

[charliec]

Can you just make it simple for the simpleton? At each of the points in the FSM table, what ohmmeter reading do I WANT to see? What ohmmeter reading do I NOT want to see?

 

[67Dart273]

You are going to have to post (a photo) of what/ where are you referring to.

 

[charliec]

Look at the OP

 

[Dana67Dart]

Can you just make it simple for the simpleton? At each of the points in the FSM table, what ohmmeter reading do I WANT to see? What ohmmeter reading do I NOT want to see?

0 good greater than 1 not good.

 

[charliec]