wrench and battery question

[CL8]

1. Am I correct in thinking you would get burned quicker by touching a wrench to the positive and negative terminals of a car battery than touching the wrench to the positive battery terminal and metal on the vehicle, because the wiring on the chassis gives resistance, and terminal to terminal gives very little if any resistance?

2. Where is the wiring on the body of a vehicle placed?

3. Are there wrenches made with rubber around the handle to prevent
accidents and severe burns like this?

thanks
cl8

[shorod]

1) In theory, yes, there would be slightly more current available going direct from terminal to terminal than the chassis. In practice, the 2 or 4 gauge wire and clean connections will offer so little resistance that it would be negligible with so much current capacity.

This is the reason that on a negative ground vehicle you always want to disconnect the negative connection from the battery first, that removes the potential (pun intended) for shorting the wrench to ground when removing the positive cable. Many of the newer vehicles incorporate some type of cover for the positive cable to further reduce the chance of letting some conductive piece from shorting across the battery terminals, including a wrench when removing the negative cable.

2) I don't understand what you're asking here. Wiring is placed in the vehicle anywhere it needs to be placed to get to a common fuse/relay panel (often more than one panel in newer vehicles), the starter, alternator, etc. Other than placing wiring to complete a circuit, I wouldn't say there is necessarily any standard from one vehicle to the next. The only standard is probably the way airbag system wiring is covered (typically orange loom/tape, but I'm not even sure I'd say that's standard) and now they're starting to standardize the covering and routing for the high capacity wiring for hybrid and electric vehicles.

3) For side post battery connections, yes. Most of the ratchet wrenches for these have a plastic sleeve over the handle. For standard top-post connections I'm not aware of any, nor do I really think they'd sell. Often there is little clearance for the wrench head already, adding a plastic layer would reduce the swing of the wrench even further. Plus, the only people that would likely consider buying such a specialized tool would be avid DIYers or professionals. Avid DIYers and professionals typically understand the dangers and know how to avoid them to feel that it's worth buying another specialized tool that they will rarely use. Instead there are covers for the positive terminal at the battery.

-Rod

[CL8]

Thanks Shorod! you've been a great help in answering my questions!

Of course I'm not very knowledgeable in auto electronics, or any electronics,
But my question about wiring was because I've been told any metal on the vehicle is connected to ground,
and that connecting wire to the chassis means less wiring elsewhere around the engine,
So wiring for the electronic gadgets (I suppose) must somewhere be attached to the metal frame of the vehicle,
so I was wondering WHERE normally those points are.
For instance, the radio wiring in the average vehicle, how would it be connected to the chassis?
(There might still be something I am missing in this)


Thanks
cl8

[RahX]

MOST of the wires on a normal vehicle carry some sort of current and you wouldn't want to haphazardly ground them. Quite a few are computer controlled/monitored so it is all but essential to isolate them from other wires. A lot of ground wires share a common grounding point so tracing and them is a lot easier. If you had a dozen different grounds all grounding at different points, testing a ground would be a test in patience at the very least. Usually if a ground goes bad you can safely assume it is isolated as long as it doesn't affect more than one system. Multiple system problems could be caused by a bad ground if they share a common ground. Your vehicle can be improperly grounded. Most drivetrains are rubber mounted from the engine to the differential. The same goes for the body and frame(if applicable). You have to ground the engine to the body to the frame and do it quite a bit to keep from having problems. It is very easy if you get some schooling on the subject but that doesn't mean it still isn't complicated

[CL8]

Thanks Rahx.

So, would that "grounding point" normally, on the bottom part of the frame, the top, the right, the left, the front, the back....?

Say on a Toyota Corolla, where on the frame is the ground strap, as I think it's called, connected?

Thanks, cl8

[RahX]

On a Corolla there should be a few from the body to the engine, there is no frame. As for where it is at, you would have to look it up. They aren't hard to spot for the most part and there is no real method for attaching them. Just an open bolt hole on the engine and one close to it on the body.

[shorod]

You'll often find them going from the head to the firewall and from the block either to the head or block to firewall. In many modern cars the firewall is part of the unit-body, aka unibody, which replaces the old school frame. The purpose of the common ground points, besides having a common point, is also to reduce ground loops which can also introduce noise in to electronics such as the radio and computer controlled items. Another precaution against noise is to shield the wires for noise-sensitive circuits. And, again, these methods and locations will vary from vehicle to vehicle. About all you can safely say is that the battery will be grounded to the engine and the chassis, and the electrical devices will also be grounded to the engine or chassis.

-Rod