Fun with OHM meter... Legacy has piss poor grounding?

This weekend I decided to test resistance between a few points of the car for a possible future audio install.

There seems to be some piss poor grounding from the chasis and the motor to the negative terminal of the battery.

When testing the connection between the negative terminal of the battery and the chasis I got a very poor 2.4 ohms of resistance. I checked this multiple times at diffrent locations each time. When I checked the resistance from the negative terminal of the battery to the motor I got 2.5 ohms of resistance. I also checked and rechecked this multiple times to make sure I wasent dreaming.

When testing 2 points on the body the Resistance was a very good 0.01 ohms of resistance. When testing points from the motor to the chasis I got a similar result anywhere between 0.01- 0.02 ohms of resistance.

This is very odd. There seems to be some sort of problem grounding from the neg terminal of the battery to the chasis. Which in itself is very odd because there are 2 very thick cables providing grounds.

The wires that come directly off the battery looks to be about 8 AWG to the chasis and 6 AWG to the starter motor/ tranny ground points.

The chasis ground comes directly off the battery clamp loops around the main fuse box and attaches to the drivers side shock tower. No more than 1 foot away. The Starter/ Motor/ Tranny ground dips into the engine bay and makes a connection next to the starter motor on a grounding point on the block.

2 VERY short runs of heavy gauge wire and still 2.4 ohms of resistance? I should be getting no more than 0.01 ohms?

Then I start thinking maybe there is corrosion on the terminal/ ground points. I check and they seem pretty spotless.

I dont know what the cause of this is but the OHM meter shows VERY high resistance between 2 points where there should be NO resistance.

I wonder if this could be the cause of some of the stuttering problems or electrical gremlins that a few of of us are experiencing.

I suspect that there may be some weird galvanic micro corrosion between the materials used for the wire terminals and the material they used to coat the chasis. Since we are dealing with direct current and the negative terminal is an Anode such a conclusion may not be too far fetched.

In the next few weeks or when I find time. I will make my own custom grounding kit with gold plated connectors to see if this actually makes any diffrence. I will try to connect points that have higher than normal resistance.

i've heard both "extra ground wires help", and "extra ground wires do nothing".

at the very least you can clean off the contact points with a wire brush (and remove any paint, if there is some at the contact point) and cover the connection with dielectric grease to prevent corrosion.

you can make your own grounding kit with some connectors and bulk wire from Home Depot, but with the ebay grounding kits being so cheap, its almost not worth the effort.

for $20 or so for the ebay kit, it can't hurt, especially if you are having stuttering problems. getting more accurate readings from the various engine sensors can't hurt, either (they report in the milli-volt range.)

Update...

Soldering 5 peices of 10 gauge wire into a 0-gauge gold plated audio connector takes up alot of solder and a LOT of heat. Screw an electric iron. The only thing I found effective was an AIR/MAPP torch.

I just used up half a roll of pure silver solder... I feel poorer already.

At least I can say its a super strong joint. Theres at least a half ounce of silver in the connector head

Im a bit skeptical of the EBAY kits and even the $150 HKS Circle Earth kits thier connection points are kinda arbitrary. Im pretty sure they never measured resistance between 2 points of the car to determine the resistance.

Ill keep you guys posted. Im still trying to find the optimal grounding points. Hooking up a ground terminal to somthing that dosent require additional grounding is pointless. I see all these cars with grounding wires hooked up to thier shock tower Im sure your rubber insulated shock tower needs ALOT of grounding

I do know for sure that one ground wire is going to the interior and will bolt to the ECU cover or a solid point near that area.

The other will go to the drivers side and mount to the dashboard subframe as alot of electronics ground to this point.

One will also go to the alternator case/ mounting brackets.

Im still trying to determine the best place to put the 2 other engine ground points.

or do what the JDM race companies do:

Ground every negative terminal that they can find, including all spark plugs using 10-gauge each.

I'll double check later, it just seems that the car has a lot more wires... and we all know the longer the wires, the more resistance you have to deal with, so we can shorten the distances with break-points of grounding it in more local places. Daisy-chain the sucker and you're set.

I will be doing this as soon as put in my UTEC.

I would only daisy chain with very heavy wire. Connecting wires in series increases resistance whereas connecting wires in parralell decreases resistance.

Yea, 4 and 6 ga

Running things in parallel is definitely the lesser of the two evils when it comes to power-robbing.

And watch the daisy chains - ground loop hell if you suddenly find a place where the body resistance is low...

RobY - thank you for doing this!! But I am still gun shy talking about earthing on our cars, there are just too many peeps who know so much about it (I suspect without every testing anything).

Good stuff! Hope this helps some people with their little 'leccy niggles.

Update... I ran to best buy during lunch but im not paying 5 dollars for a pair of connectors.

If anybody wants to try thier hand in this http://www.thezeb.com has gold plated connectors and audio power cable for really cheap.

Right now I am awaiting delivery of some much needed parts.

Update... I ran to best buy during lunch but im not paying 5 dollars for a pair of connectors.

 

If anybody wants to try thier hand in this http://www.thezeb.com has gold plated connectors and audio power cable for really cheap.

 

Right now I am awaiting delivery of some much needed parts.

That company looks good, this one that I have use plenty of times also has good prices:

http://www.darvex.com

And their customer support is great.

X

.........The wires that come directly off the battery looks to be about 8 AWG to the chasis and 6 AWG to the starter motor/ tranny ground points..........

What was the measured resistance of the 8AWG battery cable?

A very odd 2.4 ohms... Which makes no sense whatsoever. Unless of course I am tracing a diffrent cable completely.

Ill verify my findings when I get the parts in.

Still anywhere on the chasis at 2.4 ohms resistance is high.

I'll check the resistance on my car when I get home and post the results.

I already modified the ground just to see what I am getting.

It would be nice to get a second set of numbers from a non ground modified car.

I will post up pictures this weekend if there arent any here by then.

I use 4 Gauge ground cable (black) from the a local car audio joint and used their 4 Gauge ring terminals. ACE Hardware has them for $1.25 non-insulated

(-) terminal on battery to stock chassis ground location

passenger side strut tower to engine block I may do some more I just used the stuff off of my WRX.

OK, well with my current grounding mods I got readings of <.001 at all points.

I am curious if someone else is able to recreate the high ohm readings that Roby got.

OK, well with my current grounding mods I got readings of <.001 at all points.

 

I am curious if someone else is able to recreate the high ohm readings that Roby got.

The photo of your multimeter shows that you have the meter set in diode-testing mode. The displayed value is in volts, not ohms. Take it off the diode setting, and set it at 200ohms, and then see what resistances you have in the ground wires.

A very odd 2.4 ohms... Which makes no sense whatsoever. Unless of course I am tracing a diffrent cable completely.

 

Ill verify my findings when I get the parts in.

 

Still anywhere on the chasis at 2.4 ohms resistance is high.

Have you totally disconnected the car battery before making the resistance measurements?

Have you totally disconnected the car battery before making the resistance measurements?

nope. I figure it shoudnt matter since i am not completing any circut by testing 2 ground points.

nope. I figure it shoudnt matter since i am not completing any circut by testing 2 ground points.

If you are, for instance, placing the meter probes at the neg battery terminal and the end of the neg battery cable (where it is grounded to the motor or chassis), and all the wires are still connected to the battery at both terminals, then you are measuring the sum of two parallel resistances. One resistance being measured is the obvious one, that between the neg battery terminal and the cable ground point. The other resistance path being measured is that between the neg battery terminal, through the battery plates, through the pos battery terminal, through whatever else is still in the circuit (e.g. radio memory, immobilizer, etc), and then back to the cable ground point.

You should disconnect the cables from at least one of the battery posts before doing resistance measurements. This will also positively protect your ohmmeter from potential damage.

The photo of your multimeter shows that you have the meter set in diode-testing mode. The displayed value is in volts, not ohms. Take it off the diode setting, and set it at 200ohms, and then see what resistances you have in the ground wires.

Thanks, wrong picture