Can a 4 prong relay be used to trigger a ground?

[G50]

I’m trying to use a relay to trigger a ground connection.

In my hand drawing, the wires coming into 87 and 30 complete a ground (or a circuit) that triggers a separate fan relay.

So as I understand it, when I put 12v into 86, it should close the relay switch, and complete the circuit between 87 and 30.

When wired like this, it does work. For a while. But the relay fails after a short time.

I figure I must be missing something. I know it’s not the normal use of a relay, like shown in the diagram, in that it’s not triggering a higher load circuit, but in my feeble electrical mind it should still work.

[908/930]

How many amps does your fan pull? What is the relay rated for? Likely the relay is not rated for enough load.

[masraum]

Just to be sure I understand, you've got 1 relay triggering a second relay, not providing power for the fan motor, right?

[G50]

Originally Posted by masraum

Just to be sure I understand, you've got 1 relay triggering a second relay, not providing power for the fan motor, right?

That’s correct.

It is completing the circuit of the temp sensor on the radiator. Those are very thin wires, triggering the high speed fan relay (the fan uses huge wires).

Originally Posted by 908/930

How many amps does your fan pull? What is the relay rated for? Likely the relay is not rated for enough load.

The fan pulls big amps, the power wires for it are huge. But see above. That should make the fam motor amps irrelevant, right?

[G50]

The top sensor is the high speed fan sensor. The wires piggybacked onto it are going into 30 and 87.

So when the relay is activated (or when the temp gets high enough to close the sensor switch), the high speed fan relay is triggered.

[908/930]

Could be an arc is being created in the first relay points from the coil in the second relay, is this being switched a lot? Could try a small varister to ground to help the voltage bypass the relay. If that is what is happening. If you just touch the wire to ground to turn on the second relay and pull it away does it arc?

Edit, your last post just arrived in, so you are burning out the temp sensor contacts? If so same load related problem.

[G50]

No arc.
(30 amp Bosch relay, btw)

[908/930]

How many milliamps does the relay coil use? Any idea what the current the temp sensor is rated for?

[G50]

Idk if I’m burning out the temp sensor contacts, the car never gets anywhere near hot enough to trigger it.

[G50]

[G50]

Originally Posted by 908/930

How many milliamps does the relay coil use? Any idea what the current the temp sensor is rated for?

I don’t know, but I can try to figure it out.

I’m guessing it has something to do with my piggybacking the wires like that.

[908/930]

Can you do a quick sketch of the entire circuit. Sounds like you have a manual switch two relays and temp sensor all working together?

[G50]

This is my understanding.
The X wires are added by me.
The Y are existing.

[G50]

I do have a manual switch, shown on the left.

All of this complication is caused by my determination to have the switch light up when on. So the switch has 12v going into it for the bulb, when I press it in, it turns on the bulb, and also sends 12v to the relay.

[G50]

It actually does work. I press the switch in, the internal light goes on, and the fan is triggered.

But it seems to kill the relay eventually.

[908/930]

That should work, I don't see why that relay would not last. Looking at picture of your temp switch I see a red wire, that is not a positive is it?

[masraum]

So you have 2 ways to trigger the fan, the temp switch AND a manual switch (parallel)?
Or is it that both have to be engaged for the fan to come on (series)?

[G50]

Originally Posted by 908/930

That should work, I don't see why that relay would not last. Looking at picture of your temp switch I see a red wire, that is not a positive is it?

No, that’s one of the wires coming from my added on relay. (Probably should have used another color),
In this picture, the 2 disconnected wires on top are the factory temp switch, the bottom are the 2 from my relay. They are piggybacked at the temp switch.

[G50]

Originally Posted by masraum

So you have 2 ways to trigger the fan, the temp switch AND a manual switch (parallel)?
Or is it that both have to be engaged for the fan to come on (series)?

It’s parallel.
When I hit the dash switch the fan comes on, no matter what temp the radiator switch is at.

[908/930]

Is the contacts that fails on that first relay? If so I'm still thinking you are getting some voltage spike back from the fan relay coil.