Question about 1999 Saturn SL

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Which sockets on fan relay are power ? what are they all for? any diagrams available

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Your car is constructed with many electrical relays. These control relays are used like a switch that utilizes an electrical trigger signal to activate. Once a relay is activated it will connect an electrical supply to a particular accessory. These accessories can range from the main ECM (computer control) to a fuel pump. Most control relays work on the same principle even though their terminal configuration can vary slightly. There are two tests that need to be considered when dealing with a relay problem. Is the problem with the actual relay or the power, ground or trigger circuits that activate the relay. In this car repair guide we will test the relay contacts, operation and activation circuits. A relay is more prone to failure when it is warm. A rely can be considered into two separate halves. The first or primary half of the relay utilizes an electromagnet to close the secondary electrical circuit inside the relay. This electromagnet is activated by a simple power (+) and ground (-) much like a light bulb circuit. The second half of the relay is the "switch" that controls the power to a particular accessory like a fuel pump or ignition system. So, to re-cap, if you activate the primary side of the relay (electromagnet) it closes the contacts (switch) to supply power to operate an accessory. The relay primary side activation can be done manually, example: headlight switch on the dash activates the headlight control relay to supply power to the headlights. Or the relay primary side activation can be done automatically, example: When the ECM (computer) commands the fuel pump to turn "on" it will send an electrical signal to activate the fuel pump relay. The secondary side of the relay is the "switch" and does exactly as it is described; turn "off "and "on" power to an accessory. The guide below covers the most popular wiring configuration. Most relays are located in your car's fuse or power distribution center, to find a particular system relay for your car consult your owner's manual or a car repair manual.

which sockets on fan relay - 94fbc56.jpg

Relay Terminal Identification

  • Terminals 86 and 85 are the primary half of the relay that utilizes an electromagnet to close (connect) the secondary electrical circuit inside the relay. This electromagnet is activated by a simple power (+) and ground (-) much like a light bulb circuit.
  • Terminals 87 and 30 are the secondary half of the relay that is the "switch" that transfer's electrical current from one terminal to the other.
  • Terminal 87a is not widely used and does not need to be connected for the relay to operate. 87a can be used for many different things such as relay activation monitoring or connecting a separate circuit that uses power when the relay is not in use.
Common Problems:
  • As the relay heats up in normal operation, the electrical contacts inside the relay can short circuit causing the electrical flow to stop. When the relay contacts cool it will resume the flow of electricity. To test for this problem attach two test lights to terminal 30 and 87. Attach the test lead to the both terminals, a small piece of wire works well for this. Reinstall the relay and monitor the test lights while in operation. If one of the test light bulb goes out while in operation replace the relay. If both test lights go out trace the main power supply to that relay, consult a wiring diagram from a car repair manual and repair as the short circuit as needed.
  • If too much amperage is being drawn through a relay circuit it can cause the relay contacts to "stick" not allowing the power to be shut off to the accessory. Example: When an ABS system motor ages it will draw excessive amperage cause the control relay to "stick". This condition will run down the battery in a short time until corrected.
  • Moister can get inside a relay hindering the relay operation.
  • While testing for power, ground is contacted causing the fuse for that circuit to fail.

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Posted on Jul 03, 2010


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