4th Gen Floating/Bad Ground?

[TeryT]

Here's something that might interest some of you. I had recently installed a tranny temp gauge & auxilary tranny cooler/fan. I was getting funny readings when the gauge read around 200 degrees, and when I would turn the fan on & off. The gauge & fan are two seperate systems, with seperate fuses, grounds & wiring. I noticed that the digital gauge would start reading wildly varying temps when I either turned the fan on or off.

So I began to suspect a grounding issue. In checking where I had grounded the gauge & the switch, under the dash, I found there was about 6 ohms resistance between this ground bolt & the negative battery terminal. I then checked from the body grounding right beside the battery, and still had over 5 ohms resistance.

Upon checking the engine, I found the engine had 3 ohms resistance between it & the negative battery terminal. None of this seemed right, as there are straps that are supposed to ground the engine, body & negative battery terminals together -right!?

So, I ran a wire from the gauge sensor ground, up under the dash, directly to the negative body terminal. Now I get readings between all grounds (battery, body & engine) of under 1 ohm.

So you might check with a digital ohm meter to see resistance between your negative battery terminal & the body/engine. My thinking is that the resistance should be negligable - under 1 ohm. Sensative electronics, such as my tranny gauge, could be effected. I'm wondering what else might be effected as well - trip computer or JBL digital stereo perhaps?

I will report back when I take her out again & see if the new grounding wire helped the wierd tranny gauge situation.

Thoughts?

 

[Larry]

You are right to be concerned about bad gounds. In a worse case, if there is an open ground between the alternator and the battery it will 'fool' the regulator and keep it charging far too long at elevated levels, sometimes to the maximum ability of the alternator, with voltage far too high for anything in the system. This kind of stuff cooks both the alternator and battery, and can damage anything in between. If bad grounds are hard to find, you have to make your own, with extra ground straps. I had to add them to my Audi which had a really poor electrical system. After three batterys and two alternators and some gauges, covered under warranty, I added straps between the alternator housing-block-battery and headlight buckets and the fuel pump. I also added a seperate fused connection for the fuel pump. After that all electrical problems ended. The electrical system in that Audi amounted to a self-propelled fire trap.