544DRS

This is the fourth of several "stupidly simple questions" I'm embarrassed to ask. Search function didn't return "stupidly simple" enough answers...my .pdf workshop manuals don't cover this either.

My 944 is stripped and I'd like to get it back together, after painting and some rewiring, plus after installing a kickin' stereo. That's where this question originated.

Are the five or six grounding points on a 944 "connected" in some way?

As I researched car audio, I found that many installers like to have their grounds tied to the alternator case or to the negative battery terminal. On one forum, I read that Audi and Porsche cars have galvanized bodies (or was it chassis?) and that was a reason to be sure the audio's ground goes to the alternator case or negative battery terminal.

Going further, I know that some of my 944 electrical issues are aggravated by poor ground connections. If the ground points on my 944 aren't tied to the alternator case, for instance, would doing this help alleviate some electrical problems involving poor grounds?

Thanks,

Nick

88BlueTSiQuest

Yes, they are all connected via the car's body. If you look at the ground points, you'll see that they welded in a plate for the ground bolts. In order to weld that piece on, the galvanization had to be stripped for a clean weld. Galvanization is only skin deep, so under it is still highly conductive steel.

As to the car audio ground aspect.... Well, I was an installer for the better part of 12-14 years, held an MECP Basic, and MECP 1st Class certificate, and this is the first time I've ever heard of anyone grounding a system to the alternator... Heck, I've only grounded systems directly to the battery on a couple of occasions(all of which had to do with a rear mounted battery on dual alternator systems or battery isolated systems).

Here's what I did. Reinforce the factory ground wire at the battery. If you look, I believe that Porsche merely used a 6g ground there for the bulk of the car electronics. This is fine for the car itself, it it's stock form. But when adding a large stereo system, that little ground wire becomes the weakest link in the whole system. If you run 4g from the battery to the amp, then you need to add a 4g run from the battery negative terminal, to a good ground point(the same point Porsche used is fine). At the back of the car by the amps, find a good place to put your 4g ground off of the amps(distribution block), make sure it's cleanly sanded and use a nut/bolt to attach the wire. I would sometimes use seatbelt bolts, as they are strong, and will allow you to torque down the wire.

JimV8

The basic concept of a DC (direct current) circuit is ground (earth) as the brits would say. The 944 find earth from the battery to the engine block and from there to the frame and from there it goes on and on. The problem is corrosion. When the connections corrode resistance goes up and voltage drops and all kind of things go wrong, go wrong, go wrong, such as the fuel guage reading 3/4 when the tank is full. This happens all along the path. Making a good ground means going to the bare steel and using dielectric grease. Its not rocket science, but it's close.

544DRS

Thanks for the posts. This all makes sense to me. I'd never heard about "alternator grounding," but with my limited understanding, it seemed plausible. Still, like most things I learn from the Internet, getting the idea corroborated on another forum, website, and so forth makes me feel better. Here's where I read about the alternator grounding...

http://www.the12volt.com/installbay/forum_posts.asp~TID~73496~PN~1

"When measuring for resistance to ground, it is always best to use the case of the alternator as your reference point. This is absolute ground when the vehicle is running. I also find it better to use an analog meter for this purpose since analog meters allow you to "zero out" the meter to accommodate for the much longer than usual test leads needed to make such measurements and eliminate the resistance added by the extended test leads from your readings which provides you with a more accurate measurement and a zero ohm starting point. Doing this, you will see resistance levels much closer to zero than you will with digital meters without this "zero out" feature. Also, when replacing or adding a new ground from the engine to the vehicle's chassis, you should always use the case of the alternator as the engine connection point."

Mamooguy

Here's the grounds diagram, in case it's useful:

88BlueTSiQuest

Yeah, that uhm.... Makes no sense what-so-ever.

The battery is the source of ground on a vehicle. It's the connection from the negative terminal to the chassis that completes the circuit.

The alternator uses it's outer shell as a ground, which is merely bolted to the engine, using the engine block as it's conductor of ground. You'd be hard pressed to find a wire that has a lower resistance than that of the complete alternator shell to engine resistance. Then there is generally a 6-4g wire, that grounds the block to the chassis of the car, which ultimately makes it's way to the battery.

If the alternator was the heart of the grounding system, as the above suggests, then why don't we have dual lug alternators? You'd think there'd be a big nasty ground lug sitting next to the power lug. Heck, just to really pay attention to how 'important' the alternator is, look at the size wires attached to it to begin with. Normally most cars use a tiny little 8g wire for the charging wire to the battery.


As I had mentioned, beef up your battery main ground, and be sure to have a nice solid ground wire at your amps, and you'll be fine Looking at the thread you posted, the original topic starter suggestions are valid.

544DRS

Thanks. Good to hear. I just located a 2-gauge negative battery cable. I'll start there.

Nick

philcav7

Cars can run without the battery, the alternator is the heart of the electrical system.


Most installers will recommend using a grounding point in the rear of the vehicle for an amplifier installation. Rarely do you see a ground ran back from the battery or alternator to an amp. Reason being, as mentioned above, the vehicle frame/body is a massive hunk of conductive metal with a low resistance value.
Most importantly, make sure your grounding contacts are clean and secure. Make sure your battery terminalss are clean. When installing your ground from your amp, make sure you sand the paint away to bare metal. I am not too sure why the galvanized body would create problems with the grounding, perhaps bi-metal contamination becomes an issue at the grounding points.

88BlueTSiQuest

Question here is, have you tried this? I've never pulled both terminals off of a battery in order to run the car directly off of the alternator.

The alternator and battery live a symbiotic life, and depend on each other for proper operation.

We all know pulling the positive cable from the battery was the old school method of checking alternators, but the question remains... What happens when both terminals are disconnected?

ccaarmerciill

i dont know, but I did have a friend that tried to jump start his jetta with his cell phone battery and some gum...
odly enough it started up next try...
but I have a feeling it wasn't the battery

75ohm

That's a great McGyver move right there but there's not enough amperage in the cell phone battery to power a pissant motorcycle 100 feet.

knfeparty

Why is this not a sticky?! Geez I've seen so many people struggle to find them all (myself included) and this would have helped a lot.

Bri Bro

It has the same result, it disconnects the battery. Disconnect the positive, disconnect the negitive or both has the exact same result, the battery is out of the circuit. And with all the computers/electronics in cars, pulling off the leads to the battery with the car running can generate a voltage spike that can toast electronic equipment and can be very expensive.

Old car didn't have computers, ignition modules, ABS etc.

544DRS

Just wanted to return to this discussion and show some photos from my car's grounds.

First, here's the negative battery terminal, along with the "auxiliary" negative battery terminal the previous owner provided:

Negative and "auxiliary" negative battery cable

I would think a ground wire would want to tie into the bolt used to fix the cables in the battery tray to the wall.

Here's a picture of the bolt looking lonesome (I used a rubber glove "finger" to point at the bolt extruding from the wall).

That pink battery cable runs from the negative battery terminal to here...

Here's a reverse image shot of that connection...

A rusty cable ties the ground to the engine block.

Would you trust this cable?"

Especially now?

Especially now?

What was especially sad was seeing several ground wires, wires that probably serve important 944 functions, stuffed wherever they might fit...

Wadded ground wires "

Hope you find the pictures enjoyable,

Nick

544DRS

I'm good with the sketches, but what does the "position in vehicle" columns numbers mean?

Thanks,

Nick