Knight Switch

[puddle jumper]

I'm going to install a knight switch on my Spectrum.
What im thinking is to install it on the negitive side of the battery so i don't shock load my electronics when i turn it on. Lots of automotive electronics are switched on the negitive side for this reason.
My problem is every boat Ive ever seen has the knight switch on the positive side. Is there a reason for this?
I'm looking forward to you guys input.
Thanks
PS im using an marine sealed switch

 

[Silvertip]

Re: Knight Switch

Boat power systems do not have any switches in the negative side of the system. Power on is power on regardless which side of the system it's placed in so "shock loading" is the same regardless. As for car electrical systems, the only negative side switching are some ECM controlled circuits and some sensors -- and it is not done to prevent "shock loading". It is done out of convenience. Why run two wires to a switch such as a temp switch for example. That sender is simply placed in the ground side to eliminate one wire since the sender shell is already grounded. You don't have that luxury in a glass boat for example. Wire it the way it is supposed to be wired so the next person that ends up with your boat doesn't have to figure out what the heck you did.

 

[puddle jumper]

Re: Knight Switch

Silvertip you are thinking old school. Most sensors in the new cars just about all have two wire going to them. As a rule thay have a 5 volt reference with a variable reference back to the ECM. Only some of the gage sensors have the one wire.
I guess what im thinking is when ever you hook up electronics and you read the owners manual thay always seem to say
hook up the power first and the ground last. That's why im thinking of putting the Knight switch on the ground side.
Now becouse there will only one wire coming from the battery negative to the knight switch it should be very easy for some one to figure it out. If not thay should not be buggering with it and get help.
Any other takers

 

[drewpster]

Re: Knight Switch

I, like Silvertip, have only seen switches placed on the positive side of most circuits. (non-ECU, ICM, or ECM, MCT ect. digital switching)
I have seen one exception but it was not a marine application. The newer model Kenworth tractors (semi) have their switches almost exclusively on the negative side. I am not sure why, and I never got an explanation that made sense from my boss.
Personally I prefer having switches on the positive side as close to the power source as possible. I hate the idea of having long runs of live wire.

 

[Silvertip]

Re: Knight Switch

The 5V reference circuit is used in a variable resistance circuit such as a coolant sensor that ultimately displays temperature. Those circuits require a separate ground (actually called a return) because they go to either of two places: 1) a common ground to avoid ground loops which messes with electronics, or 2) the return is dedicated to the driver for that circuit. The circuits I'm talking about earlier are the idiot light sensors that are merely switches so in that respect it is old school. The grounding temp sender for the overheat alarm on an outboard is another example. EFI/DFI engines obviously have an ECM so they use the same return switching scheme as used in "new school cars" because of the ECM. There was a time when some cars and trucks used positive ground as well. Doesn't make it wrong, but the engineers finally got their heads together and decided a standard approach is the way to go. As for shock loading, in which wire do you suppose the power switch is located in your electronics? If shock loading as you call it was an issue, don't you think they would switch the negative side?