Wiring for Dummies - Grounding questions

[Traveller]

I know just enough about wiring / electric work to be dangerous, so I am moving slowly and carefully and asking for all of your help to keep me from accidentally burning the car to the ground!

I am now installing the Ron Francis and Coyote harnesses and will be adding a few more circuits to the rear of the car (trunk light, possibly backup light, seat heaters). I have found some unused circuits in the RF fuse panel which will work well for my purposes, so now I am running the extra wires to the back of the vehicle. I am opening up the RF rear harness to add these wires going to the back and then putting it all back into the rear harness convolute. Obviously power wires need to be run from the fuse box back to the end points. When it comes to the grounded side of each new circuit, is it best practice to splice onto the existing ground wire in the rear harness, or is better to add a new ground to chassis somewhere in the rear of the car and ground the new circuits to that?

It would seem that the second option may be safer so as to not overload the current ground wire in the harness with the new load.

Thanks,
Jason

[rich grsc]

Ground to the frame, just be sure get good metal to metal contact.

[Traveller]

Ground to the frame, just be sure get good metal to metal contact.

Thank you, Rich. Will do.

[CraigS]

Bingo. You are exactly correct. Some times we forget that an electrical circuit is a loop and therefore the ground wire needs to be the same gauge as the power wire. And, even though it may not happen, if everything on that circuit is on at the same time, the amp draw adds up.

[Traveller]

Bingo. You are exactly correct. Some times we forget that an electrical circuit is a loop and therefore the ground wire needs to be the same gauge as the power wire. And, even though it may not happen, if everything on that circuit is on at the same time, the amp draw adds up.

Great. Thanks for the confirmation Craig. That will save some space in the harness running down the trans tunnel.

- Jason

[GTBradley]

Grounding to the frame is always a good option. Just think about the type of metal you’re grounding to and verify that the circuit is complete with a multimeter. I have grounded small, after market electronics to the inner, aluminum panels without issue, but a large load there would not be appropriate. When grounding to frame, it’s best to grind off the powder coat for a good connection, but for a long term good connection you need to consider corrosion. Some dielectric grease will protect against future ground fault issues especially in areas that are exposed to the elements.

[BEAR-AvHistory]

Just make sure you grind off any coating on the frame that will be under your terminal.

Edit sorry missed GTB's post so I will just second him +1

[rich grsc]

I was sure I said to have good metal to metal contact.

[Traveller]

Thanks everyone. I will make sure I have good contact.

[John4337]

I used a Ron Francis grounding bar for all the stuff behind the dash, runs from battery negative post.

John

[Fixit]

2nd all of the above, with a few adds and items for thought...

- It was mentioned about it being a loop, and overloading the "ground/return" wire. True... but, (depending upon what you're adding) consider the probability that not everything will be "on" at full load at the same time. An additional ground may not be needed, tapping into existing will be fine.
- Adding multiple grounds at different locations can induce problems. Consider running added grounds back to a central/common point convenient to all devices, and make it accessible.
- Absolutely on the "bare, metal to metal contact"!
- Pick up an assortment package of "star" lockwashers. Get the ones that are both internal & external. 6750040-23.jpg They'll bite into the metal and ensure a good connection.

[Traveller]

Thanks John. All great points.

2nd all of the above, with a few adds and items for thought...

- It was mentioned about it being a loop, and overloading the "ground/return" wire. True... but, (depending upon what you're adding) consider the probability that not everything will be "on" at full load at the same time. An additional ground may not be needed, tapping into existing will be fine.
- Adding multiple grounds at different locations can induce problems. Consider running added grounds back to a central/common point convenient to all devices, and make it accessible.
- Absolutely on the "bare, metal to metal contact"!
- Pick up an assortment package of "star" lockwashers. Get the ones that are both internal & external. 6750040-23.jpg They'll bite into the metal and ensure a good connection.

[totem]

2nd all of the above, with a few adds and items for thought...

- Adding multiple grounds at different locations can induce problems. Consider running added grounds back to a central/common point convenient to all devices, and make it accessible.

True for audio, sensors, instruments and gauges. For lamps and motors, different grounds are unlikely to create problem.

The problem with multiple grounds is that high current can create fraction of volt differences between the ground points. It will not affect a lamps or a motor but may affect audio, sensors, instruments and gauges if the source and receiver do not have the same ground.