Ground Help

[xxBURT0Nxx 10+ year member]

Okay, so I'm doing the big 3 on my car right now. When grounding I am sanding the are before I put the bolt in. Problem is, when I putt the dmm on the pos of the bat and the neg I get 12.6v. When i put it on the pos of the battery and touch the other prong to the sanded area i get 0.4v. Is that okay? Or should it read 12.5ish v when it's just touching the sanded down area? Do i need to find a better spot to ground or what? Thanks!

Click to read more...

 

[xxBURT0Nxx 10+ year member]

Hold on i will take a picture because it's definitely not close... 12.6v compared to 0.4v??

 

[jrwalte 10+ year member]

Is your battery grounded to the chassis from another wire when you do this? If not, you're reading is correct.

The DMM can't ground your battery to your chassis. It only reads voltage.

 

[xxBURT0Nxx 10+ year member]

ahh.. got ya. I'll try sanding down further and see what happens. Ill post results in a min or 2... do you reccommend any particular grit of sandpaper?

 

[xxBURT0Nxx 10+ year member]

Alright, well i sanded further and now I'm only getting 0.1v so I think I need a new ground location. Here is a picture of the current ground:

Also, will the screw hole on the left work to ground the engine block in this picture:

 

[jrwalte 10+ year member]

I use a 60 grit on a dremel. Gets the job done in a few seconds //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[jrwalte 10+ year member]

You can't test the location for matching voltage of the battery unless you also connect the ground wire. With the ground wire attached to the chassis and the battery, place the DMM on the battery positive and ground chassis. You should get the same voltage reading as when you touch the battery negative.

.1 volts when testing the way you are testing is a good sign that the location will be a good ground.

As for the block to chassis ground, I just used the existing ground location and replaced it with my 0 guage.

Was that screw hole in your picture already open or did you remove the screw? Do not place a new screw into an old location that had no screw. I do believe that some are intentially left open by the engineers.

 

[xxBURT0Nxx 10+ year member]

Yeah, but I'm pretty sure my current ground is what is causing the problem. If i probe the pos terminal on the battery and then the wire that grounds the battery (when the wire is disconnected) I only get 0.6v... that's why I'm trying to find a new ground

 

[jrwalte 10+ year member]

the body of the car should act like a neg post in this case me thinks

ONLY if he has the battery grounded to the chassis by another wire. Otherwise he's touching a positive on the battery and never touching a part that returns the current to the battery to create the ground. As I said, the DMM cannot be his ground.

 

[jco1385 5,000+ posts]

ONLY if he has the battery grounded to the chassis by another wire. Otherwise he's touching a positive on the battery and never touching a part that returns the current to the battery to create the ground. As I said, the DMM cannot be his ground.

but a LOT of the cars electronics use the body as a ground.

 

[jrwalte 10+ year member]

Yeah, but I'm pretty sure my current ground is what is causing the problem. If i probe the pos terminal on the battery and then the wire that grounds the battery (when the wire is disconnected) I only get 0.6v... that's why I'm trying to find a new ground

In that test (with the ground disconnected from the battery) that is a bad grounding spot. But not because it's too low at .6. It's too high! It should read .2 or less I'd say.

 

[jco1385 5,000+ posts]

ahh, ground disconnected from the battery. i missed that part

 

[xxBURT0Nxx 10+ year member]

okay i think that makes sense.. the battery isn't connected right now and I'm getting 2 volts when I touch the wire that I just connected to that ground I made. Guess that's a good sign that when I connect it to the battery I will get 12v again?

Also, that hole had no screw in it... what if i use the one to the right of it where there is a screw?

 

[jco1385 5,000+ posts]

okay i think that makes sense.. the battery isn't connected right now and I'm getting 2 volts when I touch the wire that I just connected to that ground I made. Guess that's a good sign that when I connect it to the battery I will get 12v again?
Also, that hole had no screw in it... what if i use the one to the right of it where there is a screw?

sand it and go with it

 

[jrwalte 10+ year member]

but a LOT of the cars electronics use the body as a ground.

It doesn't matter if the battery ground is not connected in ANY WAY to the chassis. None of his electronics are connected to the battery ground to cause the ground you speak of.