Still planning my audio install , normally I'd use the chassis as ground. Can you do that on the aluminium xk? If not then where?

 

As per my opinion, negative electrical would be grounded with an alternator.

 

Huh? An alternator generates power. Why on earth (ha!! ) would I use one to ground a power lead?

 

The battery ground is behind the driver's side tail light access vent in the trunk. Along the same side under the side carpeting and at the rear wheel well arc is another ground prong (just below the trunk light).

 

As Aluminum is a better conductor than Iron and carbon both (which are obviously the building blocks to create Steel), why wouldn't you use the chassis as ground?

Vince

 

All I can think of is that aluminium oxidizes pretty promptly (it isn't destructive as that then prevents further oxidization) and aluminium oxide doesnt conduct - so you'd have sand the oxide away but also have no way of preventing it oxidizing again - creating a duff connection.

 

But to oxidize requires exposure to oxygen, so a little dielectric grease would probably solve that issue.

Vince

 

Could you guarentee though that the connection wouldn't deteriorate? Still, I was only guessing.

 

looks like your better option would be to use an oxide inhibitor (a conductive grease) to prevent any possibility of the oxide layer from reforming...

I know we use aluminum for electrical connections all over the place, so the technology is there... Being an aluminum chassis does make you take a step back and think....
I'll go crack open my aviation manuals tonight and try to read back up on the fundamentals.

V

 

Cool. I'd be interested.

Looking in the trunk (or boot in the UK!) behind the vents - there are a host of welded on earth points for us to use.

 

Be cautious. The left side is a positive connection used to jump start the car!
(You probably already knew this, but I had to say....)

Vince

 

During my install, when the installer was getting engine whine through the amp, I PM'd gn4hir (who also did his own full install), and this is what he replied:

I grounded my amp and BitOne right to the battery. And, I kept the cables short by mounting everything in the wheel well.

On most cars you can ground to any bolt screwed into the frame but.. you have an aluminum frame so there are only a few designated grounding points other than the battery. They should know this but.. check anyway.

 

OK, so to get a little further into this, I have to disagree with gn4hir's comment (referenced by bart). Chassis ground is chassis ground. There are no specific "points" on the chassis that is "more ground" than any other point on the chassis. Had we been talking about a lengthy strand of wire, I could see a variation in potential due to resistance over a distance, but not on something like a full frame of metal. It just isn't going to be that kind of issue...
This is not the same as saying that I would not have gone directly to the battery as well given his installation, and in fact I would probably have done the exactly the same.

My direction was looking into whether the OP had an issue grounding to an aluminum frame. The base answer is "no, not at all a problem". There is however the need to be more attentive to how you make your connections.

As we discussed, oxidation is a problem, and easily overcome with a sealant such as grease to minimize exposure to air and reformation of the aluminum oxide barrier. My aviation books also remind me of the galvanic (dissimilar metals) corrosion problems we get when pairing up copper to aluminum. This would be considered a no-no on aircraft. The answer is to use a sacrificial metal between the two surfaces. Galvanized steel washers are the acceptable medium and should be used to separate the two materials. The zinc coating is considered the sacrificial metal, and you avoid damage or deterioration to the aluminum chassis.

So that's the direction you need to consider should you choose to use chassis ground anywhere on the car. Galvanized hardware to separate different metals, and an anti-ox grease/sealant to eliminate further oxidation.

Hope it helps in your planning!
Vince

 

This is the ticket, available at your local ACE: GB® Ox-Gard® Anti Oxidant Compound (OX-100B) - Electrical Tools - Ace Hardware

This is specifically for aluminum or dissimilar metal connections and is conductive, unlike dielectric grease.