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

[G50]

Originally Posted by 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.

Idk. It stops working, I change the relay and it works again.

One of the times it failed, if I tapped on the relay with a wrench, it would get going.

[G50]

Is it possible I have the relay wired wrong?

If it was wired incorrectly, would it work at all (even temporarily)?

[908/930]

Your sketch looks correct. Could it work if wired wrong, well it would be able to work if the wire from term 85 (the ground side of your first relay coil) went to your other relay coil, then you would have both coils in series and your switch would energize both coils. Try a lower rated relay, there is a chance that the contacts in that 30A one do not get far enough apart. Check the wire diagram for the other relay though, does it only have 4 terminals to plug into?

[masraum]

Originally Posted by G50

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

Originally Posted by 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.

That's what I'm thinking there's an issue with having 2 switches in parallel. I can't remember what the issue is, but I've run into this before. I think having 2 switches on one circuit requires some other mechanism to ensure that you don't have issues, which is part of the reason why there's more to wiring 2 way light switches than just sticking in an extra switch.

[908/930]

Originally Posted by masraum

That's what I'm thinking there's an issue with having 2 switches in parallel. I can't remember what the issue is, but I've run into this before. I think having 2 switches on one circuit requires some other mechanism to ensure that you don't have issues, which is part of the reason why there's more to wiring 2 way light switches than just sticking in an extra switch.

I don't think that will be a problem, as long as the ground is the same for both. Different with house wire because you want to be able to turn on and off from each switch.

[G50]

Originally Posted by 908/930

Your sketch looks correct. Could it work if wired wrong, well it would be able to work if the wire from term 85 (the ground side of your first relay coil) went to your other relay coil, then you would have both coils in series and your switch would energize both coils. Try a lower rated relay, there is a chance that the contacts in that 30A one do not get far enough apart. Check the wire diagram for the other relay though, does it only have 4 terminals to plug into?

Here’s the diagram. It’s the high speed temp switch im piggybacking on.

[908/930]

80's BMW? Looks very similar to my E28 circuit.

Place an amp meter in series after your relay or at the coolant temp switch just to check how many amps it is seeing, that side is fused at 7.5A so should not be much.

[G50]

E24, so similar to your E28.
I’ll check with the amp meter, will have to wait for my new relay to get here.

[Pazuzu]

You added a physical switch, correct?

Why have a relay at all? you're "switching" the low current coil side of another relay, you can just put the switch in line and toss the extra relay.

Also, I'm concerned that what you're getting is a feedback loop. Are the new relays dying when the radiator is at high temp? You might be getting a loop where the temp switch and the relay flutter when the temp switch closes.

[G50]

Yes, it’s a physical switch.

I added the relay because the switch has a light bulb in it. I rigged it so the switch lights up when it’s activated (like a typical AC switch).

I can’t see any other way to accomplish that without a relay, but I’m open to suggestions.

[908/930]

Just checking that you are not feeding the coil of the relay through the light bulb?

[G50]

Originally Posted by 908/930

Just checking that you are not feeding the coil of the relay through the light bulb?

It’s possible that I am. It’s been a while since I made the modified switch, I don’t remember exactly what I did.

I did make a drawing at the time, but looking at it I don’t really understand the switch part. It of course made sense to me at the time, but now I’m not sure what it means. (But I suspect it may be feeding the coil through the light bulb).

[G50]

It’s an LED bulb, if that matters.

[908/930]

You show a ground wire going to the switch so you are probably ok but check it anyways. I was thinking that if you had the light in series with the relay that would limit the power going to the coil and could explain the short lifespan, light would work fine but relay would not.

[3rd_gear_Ted]

Use a current rated PNP transistor circuit for ground switching.
That is how industry does it.

[G50]

Interesting. Looks like I need to use a diode to protect it?
I’ll have to dig into this, on first read it’s above my current (pun intended) level of understanding.

https://electronicsclub.info/transistorcircuits.htm

[908/930]

One thing I do not like about transistors is when they fail they can remain on, relays usually fail off. If you are having problems keeping a relay working SSR will likely be less reliable.

[G50]

Maybe I can eliminate my add on relay?

How about wiring like the bottom diagram?

[908/930]

That should work, but the relay you have in there now should also work. With that new setup make sure you have a fuse where you pull the power for the light by the fan, or have wire rated for 30A. I still think you should try a lower 15 amp rated relay in the existing setup.

[G50]

Ok, I’ll try a 15 amp relay tomorrow.

If that doesn’t work, I’ll try the alternative wiring with a fuse.