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I have had a heater issue for a long time in my '91 Spirit, 2.5L. I turn on the heater, starts generating heat, then it cuts off and the 'Air Bags' light comes on. I turn off the heater and the light goes off. Turn it on again, cuts off, light goes on, turn off, light goes off. I am aware this would be a ground issue but admit I know little about electrical and where to look. Can anyone help me on this with some advice? I don't want to face the winter again with no defrost. I thought it might be my resistor since when the blower switches from off-low-medium-higher-highest it cuts off at the highest setting. I replaced it (mounted behind the windshield wiper fluid tank) put problem persists. I will in summertime turn it on, it blows for awhile, stops, see 'air bag' light come on, kicks back on again for a second, stops again, a couple seconds later comes back on for a second, never really stays on. In the winter when it goes off it stays off until I switch to off and see the 'Air bags' light go off too.
 

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Welcome To TD!!!

Yes, it does sound like a ground issue but you have to verify whether you are losing power or ground at the blower motor.
The HVAC control and blower resistor control the ground side of the blower motor, power is constant.

You are going to need these before you can start to trace the problem.


 

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You need to locate the blower motor, unplug the electrical connector, start the car and turn on the blower motor as you normally would.
1)Using The Digital Multi-Meter
a)Turn the knob on the meter to the 20 volt DC scale since you will be measuring voltage in the 12-14 volt range.
b)Connect the Red lead (+) to the DG (Dark Green) wire, connect the Black lead (- or common) to the BK (Black) wire.
Do not force your meter/test lamp leads into the terminals as terminal damage will occur.
Preferably You should always "Backprobe" a connector. (See Backprobing Below)
c)You should be reading battery voltage with the blower switch on High.
2)Using the 12 Volt Test Lamp/Circuit Tester
a)If you are looking to check power you connect the alligator clip from the meter to a good ground (metal surface) and when you touch the test lamp probe to power the test light will illuminate.
b)If checking a ground circuit you would need to connect the test lamp to a 12 volt power source such as the + battery terminal, when you touch the test lamp probe to a ground the test lamp will illuminate.
c)If you are looking to check for a complete circuit you would connect the test lamp as you did with the meter, if the circuit has both power and ground the test lamp will illuminate.

You can see how they work by just connecting each to the + and - battery terminals.

Test Leads/Jumper Wires
I use a long jumper wire connected to the battery and run it to the interior of the car to provide me with a good ground for testing power or a good power source for testing a ground circuit.
You can make one with 14 gauge wire and alligator clips (insulated) or buy one already made.
Jumper wires are extremely handy for checking electrical issues anywhere on the car.
Be Careful...If you connect a jumper wire to the + battery terminal do not allow the other end of the jumper to contact any metal surface, that would create a short circuit and melt/burn the jumper wire.

BACKPROBING
If you cannot get the problem to occur with the blower motor plug disconnected you will need to plug the connector back on and "Backprobe" the connector with the blower on to check for power and ground.
Backprobing means you connect your meter/test lamp from the backside of the connector where terminal damage will not occur.
This allows you to test without damage or connect to a circuit with all components connected and operating.
They do sell "Backprobe Pins", however, Paper clips also work well.
Just be careful if using paper clips, do not allow the two paper clips to touch each other, this will create a short circuit.
Picture Of Backprobing A Connector.
Backprobing the CTS.JPG


Electrical Basics

Hope this is not confusing, any questions/concerns Please feel free to ask.

 
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