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Relays

primetime

sawmill slave
Ok, to start off, many years ago I found a wiring diagram for Bosch type relays that went something like this, 30=12 volt battery power, 85=ground, 86=12 volt from a switch, 87=the load ie a fan. This is how I have my fans wired.

Lately however, I have noticed that that isn`t how other people are doing it. It seems as though most people are grounding the relay to turn them on, for instance, 85 is wired to a sending unit which appears to go to ground, which completes the circuit and turns stuff on.

I`m just wondering if I`m doing something wrong, and this is why I`ve killed two fan controllers, and why you can really tell when the fans turn on.
 

DNFXDLI

The Token Canadian
Staff member
It really doesn't matter if you switch the ground to activate the coil, or the hot.
Electrical convention is that the hots are switched so that servicing a device results in that said device being deenergized.
Switching the ground leads to power being present at the device.
I won't switch a return/neutral or ground...if fact as far as convention goes in AC circuits, it is verboten :D
It does seem that many automotive circuits are return switched though.
There is no reason your fan controller would get pooched from switching the ground.
Also...as I'm sure you know...the control (coil) circuit must be fused as well as the power circuit.
 

primetime

sawmill slave
Well that`s what I thought, but one never knows, do one? It seems everyone has a different way of doing things when it comes to automotive, and you can just about drive yourself batty looking at different wiring diagrams and second guessing yourself.

And yep, the main power into the relays is fused, and the switches are fused. Fire rocks, but not in the truck.:D
 

DNFXDLI

The Token Canadian
Staff member
Yes...fire is also best avoided in garages as well...:rofl2: :rofl2:

And yes, there are all kinds of different ways of doing things...I always switch my hots...just the way I've known forever.
 

primetime

sawmill slave
Yeah, I saw your little flashback, good times, huh?:D I`ve got a couple of my own I could tell.
 

F 150Cobra

"Wild HoRsE" Got Torque?
3,642
104
Aruba
p34215_image_large.jpg


i grounded the 85 (you could put an overide switch or thermostat there )
and i used 86 for ignition source and switch

thats how i got mine wired

you can do it any way u want i think
 
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primetime

sawmill slave
There was the time the neighbor kid and I were trying to get a riding a riding lawn mower project running, we squirted some gas in the carb, a flame shot out when we pulled on the rope, and man, who knew we spilled that much gas on the ground. Than there are the times I`ve been priming carbs with a pop bottle, spill a little, the timing is off and they pop back thru the carb, onlookers are freaking out as you blow out the flames, or if you are really lucky the pop bottle goes up in flames. There is a good time, pop quiz, what do you do with the bottle? In a garage mind you.

And Jurgen, I suppose that diagram isn`t much different than mine, except my current fan controller has a ground that isn`t switched, a switched 12v wire, and than a seperate wire for the fan. Which I have running to the 86 terminal on my relay. My relays have their own ground at 85.
 

F 150Cobra

"Wild HoRsE" Got Torque?
3,642
104
Aruba
yes me 2 same way... ground at 85 and a switched 86 :)
 

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