Need some help with amp grounds...

[Arythael 10+ year member]

I'm pretty new to the car audio scene, and I've just recently finished installing the front stage of my first build - CDT CL-61 6.5" components on an MB Quart ONX4.80 amplifier, pushing 320W x 2 @ 4 Ohms bridged - but I'm nervous about my current ground. I drive a 2003 Nissan Maxima, and I've come to the conclusion that the entire (stock) grounding circuit is pathetic.

In order to find a ground, I connected some spare wire (tested for 0 resistance over its length) from my neg. battery post to my trunk, stuck a DMM lead in the trunk end of the wire, and used the other lead to search for a good ground in my trunk. I must have checked every single piece of exposed metal and every single bolt/screw there, and they all ****! The lowest resistance I could find was 3.4 ohms on a bolt (which my amp is currently grounded to).

After discovering this, I checked the main battery ground and found 1.2 ohms in the wire about an inch from the neg. battery post and 2.0 ohms at the chassis end of the wire. Is this normal on stock electrical?

I've had a Big 3 Upgrade on my to-do list since I first started looking into upgrading my car's audio system, and it's that much more urgent after coming across this... but how safe is it in the meantime? My amp gets fairly hot, but not burning hot and it hasn't gone into protection yet. Any opinions or advice?

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[maylar 10+ year member]

First off, when you short your meter leads together you get some number (usually 0.5 ohms or so) that you need to subtract from whatever reading you get after that. If you actually get 2 ohms from the negative battery post to the bolt where that short wire attaches to the body, something is wrong. Yes, it matters and I would think your whole car's electrical would be misbehaving.

Be aware that an ohmmeter forces a small constant current through the circuit and measures the voltage then does the math to get resistance. The slightest external voltage will cause a bogus reading. If there's any voltage present - even millivolts (thousandths of a volt) - your reading is not real. A corroded battery terminal could do that.

I would double check by testing from your amp's ground to the ground point on the front fender, not to the battery terminal. Pull the amp's fuse first to be sure there's no "standby" current that could screw up the reading.

 

[All_Logix 10+ year member]

If it helps you any I grounded my everything to the engine block where my alternator grounds

 

[keep_hope_alive Premium Member]

what DMM are you using? some are inaccurate at low resistances. i insert a 10 ohm resistor in series to allow for more accuracy.

and good point about having the car on. i disconnect the battery before performing the ground resistance test.

you may have resistance through the paint where you are testing. just touching metal is touching paint. that is why we remove paint to make a ground.