How to test a switch
- Thread starter Tadams
- Start date
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use a multi meter to read resistance through the contacts. When closed should be 0 to 0.5 ohms or there about. when open the resistance should be infinite (many meters read OL)
You may need to refer to a wiring diagram to determine which connector is switched to which connector when the switch is in any particular position.
Also look for wiggly connectors sometimes the mounting of the connector becomes loose over time and will make an intermittent connection.
Good luck!
You may need to refer to a wiring diagram to determine which connector is switched to which connector when the switch is in any particular position.
Also look for wiggly connectors sometimes the mounting of the connector becomes loose over time and will make an intermittent connection.
Good luck!
Best time and easiest way to test the switches
Dfr360cuda
Diagnosis... Plum Crazy.
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Resistance will vary depending which fan speed is selected.
I'm guessing the resister crapped out and the toggle switch was installed to get the blower working.
The blower probably only worked on high after that.
Anyone with a Dakota knows that the resistor burns up every 2 years or so.
Dfr360cuda
Diagnosis... Plum Crazy.
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Can you post a picture ?
I'd guess one pin / terminal is a common and the other pin / terminals are for the fan speeds.
Check resistances from the common to all the other pins.
If you are testing only the switch there should not be any difference in resistance as (i believe) the resister is in the heater box not in the switch. Correct me if im wrong on that
67Dart273
Well-Known Member
I would not rely on an ohmeter to test either switches or rectifier (alternator) diodes or any other high power device. The thing can make contact enough to "read good" but when put under load, may heat up and give trouble. It is way way better to test under a load. "an old headlight" or something else that draws a fair amount of current is better. I would say at least 5 amps depending on what the switch is made to do.
Hook it up in a circuit with your load device, and measure the voltage across the switch contacts. It should be very low, perhaps a few tenths of one volt. The higher the reading, the "worser."
I would say most any switch, heater, headlight, etc, that reads more than .3--.4V at the most is "trouble."
"Work" the switch on/ off several times, measuring when "on" each time.
Hook it up in a circuit with your load device, and measure the voltage across the switch contacts. It should be very low, perhaps a few tenths of one volt. The higher the reading, the "worser."
I would say most any switch, heater, headlight, etc, that reads more than .3--.4V at the most is "trouble."
"Work" the switch on/ off several times, measuring when "on" each time.
67Dart273
Well-Known Member
Well that can be your load. Why not go the rest of the way? All you need to do is put a meter across the switch and read the voltage drop. Without the resistor, you can connect the motor to the other speed terminals, and it will still run "high" so you can test those switch contacts as well.
Dfr360cuda
Diagnosis... Plum Crazy.
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Correct... No resistance across the switch in any position.
The resistor in my Dakota is mounted in the duct work.
I was surprised to see how hot it got and it uses the blower to keep it cool.
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