The thermostat outputs or inputs are not described, so this is a best guess.

 

damn you guys draw nice stuffnot that anything is wrong with leve's drawing(ok maybe a fuse). but to cut down on wiring could you hook up the hotto the relay and actually switch ground it would save some wiring,cuz its alot easier to find a ground close by then running a hot to somethin.put pin 85 to hot by jumping off of pin 30 . seperate and ground motor by itself. this way you just run hot to the relay and one wire to switch and one wire to thermo-nuclear device picking up a ground close by

taco
78cj7

 

Never ever just cut the ground cicuit on relays or switches!! Do you break the neutral on your home wiring to the lights? No-you would shock your butt when changing the light bulbs. You would be the path to ground. Same with the relays or fans. You have no way to isolate the hot wire that way-sparks every time it touches ground. No big deal you say, it is only 12 Volts. How about burning the wires and causing fires, blowing up batteries, sparks around gasoline etc. Always switch the hot, a little wire is a whole lot safer and cheaper in the long run.

 

well i have to disagree with you on some of your statement. i leave the house wiring stuff out cuz you are correct, but its one of those apple and orange things to me. in my opinion(which may not be much)your way wuold run a hot to your switching devices(thermo,and master switch)so to a degree you are exposing a hot wire to the elements that could do what your saying my suggestion would do. my suggestion would not do what you said, it would only activate the ckt(relay) in question if the wires were to ground out, causing the fan to stay on which could be stopped by yanking out the relay. when dealing with some d.c. devices polarity is not an issue unless the deep discussion into conventional theory versus electron (i think thats what its called)theory is in the way.

taco
78cj7

 

House wiring is a little different. On a car, it's ok to switch the ground and won't present any hazards. Think of all the automotive systems that already work that way:
Dome light
Fuel guage
Oil pressure guage
Temp guage
Parking brake switch (for the "brake" light on the dash"
Seat belt switch (for the "fasten belt" light on the dash")
Neutral Safety switch
In some cases, the T-case switch
Motorcraft ignition (the ground to the coil is switched)

And there are probably a few more I can't think of right now.
I think it would be safe to say that nearly every car and truck on the road has switched-ground ciruits from the factory. One more wouldn't hurt it a bit /wwwthreads_images/icons/smile.gif

-Derek Schwab
'97 Sidekick Sport
'83 CJ-7

 

Yes it will work breaking the ground-it is a series circuit. The common standard on devices is to break the hot. Be it fan, relay, lights whatever. They do this for safety. Look at my profile-Professional Electrical Engineer. Why break the standard if you don't have to. If you want to pull relays to isolate problems it is fine with me. Wire your Jeep anyway you want. I will spend the extra $1 on wire to do it per normal, understood convention to people in the electrical biz. That way when the switch or controlling device is off, I or Joe car repair dude or the person I sell the vehicle to, will know it is dead. Do what you want.

 

In reply to:

The common standard on devices is to break the hot.

It is not the standard on cars. In houses, yes, but on cars, many ciruits operate by switching the ground. They come this way from the factory.
Have you rewired your cars to switch the hot on every ciruit? /wwwthreads_images/icons/smile.gif

-Derek Schwab
'97 Sidekick Sport
'83 CJ-7

 

Humm... it seems like we're flogging a dead horse. Swiching grounds has been done for years on many types of circutis. It's the norm on espically low current devices such as you find all over your house today. IMHO, switching the voltage or, more accuratly, "pulling up ground" accomplishes the same thing. The decision that I'd personally make would be depend upon a few factors:

1. How much wiring could be eliminated. Each wire and joint is a potential point of failure.
2. Would elimination of wiring expose other areas to hazzards? Safety is a prime concern on a trail rig, right up there with reliability.
3. Given the lack of a robust ground path in a Jeep, is pullin up ground a sound idea?

IMNSHO I'd still opt for enabling and disabling devices by interruption of the supply voltage coupled with the judgicious use of fuses, relays, and circuit breakers.

 

gosh your right leve time to act mature but it so easy flogging that dead horse, less chance of it kicking my teeth out the final decision and responsiblity is up to the individual. since i'm not an engennerr(heck i can't even spell it), like another poster, i guess i'm not qualified to disagree.

taco
78cj7