Needing some help on a 12 volt relay....

I am helping a friend on his Jeep today. He has a 2 speed electric fan, and were trying to wire it to work off 1 12volt relay and a 3 position switch.

I have google searched and I can not find my notebook with my notes, so I am kinda stumped... I am hoping someone here can help me.

As best as I can remember/figure is that I need to wire low speed to output 87a and high speed to 87. does that sound right??

86 is chassis ground right???

30 is 12volt power????

85 would be the ground to the switch that completes the circuit?????


Anyone know if that all sounds right??? I just need it to work like this... Up=high speed, middle is off, and down needs to be Low speed...

 

Well, I'm not sure how you're going to wire the switch. Maybe you could get it to work with a dpdt switch. I'm not sure.

Anyway, for the relay:
When it is off, 87a and 30 are connected.
When it is on, 87 and 30 are connected.
85 and 86 control when the relay is on or off.

 

Yep, those are the right relay terminals. 85 and 86 are the coil terminals. One needs positive 12v, the other is a ground.

You need to power one wire for low and one for high? I think you will need to use two relays, one for high and one for low. Since you always have continuity through 30 and either 87a or 87, how would you achieve off with just the one relay?

I would use a spdt switch like you are talking about. Ignition power to the center terminal (fused), one output to each of two relay coils. Second terminal of the relay coil gets grounded. The 30 terminals of both relays go to battery power (fused), the 87 terminal of one relay goes to high speed wire, the 87 on the second relay goes to low speed wire.

That's how I would do it.

 

I think I'd use a three position switch single pole double throw with center off position. Then the post one up.

 

I have a friend that did a single speed fan on his van. Just a regular on-off toggle switch.

He used a 50Amp toggle switch from Napa. You could get one of those in an on-off-on configuration. Then you don't need a relay. But you would have three large wires to get through the firewall, and you'd have to remember to turn the switch off when parking the truck. Alternatively, you could wire your relay inline with the center terminal of the switch and use the relay to interupt power with the ignition on/off.

 

Ya. I'm with ya there. I couldn't think of any way to wire the switch side either. In theory, you could do it with a dpdt switch, but you'd be running the full amps through the switch, but I dont think that safe/feasible with a fan and if you were going to do that, you wouldn't need the relay anyway. A double relay system will really be the only option for three positions.