Is the factory TJ frame electrically grounded to the body?
- Thread starter mrblaine
- Start date
OP
As to why you might want a conduction path between the body and frame; lightning! When lightning strikes, current flows from the body to the frame to the tires to ground. Tire manufacturers actually are required to add conductive material to the tires for this very reason. Because lighting generates very high voltages (i.e. 20kV) at low current, the conductive path does not have to be all that good (i.e. not low resistance, as Zorba discovered). Electricity at very high voltages has no problem jumping small gaps.
Also, as you may recall, if a power line falls on your car, you should stay in it until the power company can turn off the feed to that line. The car body forms a protective shell around you that goes away when you put one foot on the ground. Again, high voltage, conductive tires. It would be interesting to learn the condition of the body mounts from someone whose Jeep has been struck by lighting. I would expect some melting in that area.
On the other hand, every vehicle (ship, plane, car, Jeep) that contains iron and moves through the electromagnetic field that surrounds the earth generates charge (see Mike Faraday, c. 1850). This charge is called electrostatic and is low voltage and low current. Because there is no low resistance path to ground, we discover this charge with a static shock when we touch the door after alighting providing a path to ground through our body.
For two-way radios, the outer shield of the coaxial cable is the ground path for the antenna. If you use cheap cable with little or no "braid" you will have poor results. Also, you should run both the positive and negative power lines for the radio back to the battery and not rely on the body as a good ground path.
Also, as you may recall, if a power line falls on your car, you should stay in it until the power company can turn off the feed to that line. The car body forms a protective shell around you that goes away when you put one foot on the ground. Again, high voltage, conductive tires. It would be interesting to learn the condition of the body mounts from someone whose Jeep has been struck by lighting. I would expect some melting in that area.
On the other hand, every vehicle (ship, plane, car, Jeep) that contains iron and moves through the electromagnetic field that surrounds the earth generates charge (see Mike Faraday, c. 1850). This charge is called electrostatic and is low voltage and low current. Because there is no low resistance path to ground, we discover this charge with a static shock when we touch the door after alighting providing a path to ground through our body.
For two-way radios, the outer shield of the coaxial cable is the ground path for the antenna. If you use cheap cable with little or no "braid" you will have poor results. Also, you should run both the positive and negative power lines for the radio back to the battery and not rely on the body as a good ground path.
I don't understand the context here? Mine seems pretty well grounded at the engine block.
Edit: guess you probably mean isolated from the frame...
Meaning that although it's grounded at the engine, and engine to battery and body, for radio it sticks out like a big antenna since it's not grounded at additional points along the length.
I don’t know much about radio but I never was able to get a cb tuned well on my jeep. I wonder if a ground strap to the frame would have helped.
I’ve since gave up and just use walkies now. I don’t wheel with big groups.
I used to have a strap that went tailpipe to frame and a strap at the front and back of the frame to the body. It helped. After my build to 37s I never put it back since everyone I wheel with seems to have a different radio setup and I didn't want them all mounted and I found that if I was having a hard time talking to somebody it was most likely an issue with their install not mine..
OP
The bane of my existence leading runs. Mine works, rarely did anyone else's.
The biggest problem seems to be that there's really no way to test with certainty that your radio works without a willing friend a mile away. So people show up with antennas duct taped to their spare tire.
I have the CB mounted in mine but my last trail ride nobody had coms of any kind, and the ride before that a friend just handed me one of their handheld HAMs. I don't think I've used CB on the trail in 3-4 years. What really gets me going is when all chatter has to be relayed across 3 different types of radios and stopping to yell at the one guy who's radioless.
If everyone would agree to make the switch to race radios or just about anything standardized I'd be so happy.
B00mb00m
The Church of Cutting Brakes of Atlas-Front Digs
Supporting Member
Ride of the Month Winner
Many years ago I had a Chev S10 pickup truck that developed a noise in the manual transmission, upon removal and disassembly I found what looked like an arc strike from a welder on one of the countershaft gears. As soon as I saw that I immediately looked for a missing ground strap and lo and behold, I found a disconnected cable from the engine block to the chassis.
I can only guess at some point an electrical connection between the battery and chassis was made through the drivetrain.
I can only guess at some point an electrical connection between the battery and chassis was made through the drivetrain.
That's a good point, but even a huge wire like mine isn't necessarily a solution for that particular problem. A braid is far better for RF. Running radio power direct from the battery is good practice, but I myself am not a fan of running the negative back to it. You'll hear endless arguments on that particular subject!
Mobusaki
TJ Enthusiast
I've had success grounding CB antennas to the tub (antenna mounted above driver tail light). Of course you need to tune it with a SWR meter. I've done this on two TJs and tested a mile apart (straight line, with trees and buildings in between). I remember thinking it would be better if I grounded to the frame - turns out that may not have worked out so well. A friend tried that with his JK and his CB never worked well. Perhaps JKs are grounded similarly to TJs.
Well I was hoping you would have said 2002 as that would have coincided with moving the charcoal cannister.
I bet the one piece body on a TJ is the ONLY difference between a rusted out TJ and rusted out Taco
I looked at my 06 lJ today and it appears there is no actual frame ground on the vehicle. The engine block is grounded and the under hood loom is grounded there and the second ground goes up to the firewall. All the lighting is grounded to the body. The small braided straps to the hood and fuel filler neck are used for static discharge and radio interference. All other grounds are attached to the body from what I see. Some have suggested, brake lines steering shafts ect. In my 30 years of Automobile electrical experience I have never seen that type of thing. The steering shaft has the rubber isolator down by the box. Bearings, brake lines, and cables do not like electrical current going through them. (I’m sure you have seen this) I have seen transmission input shaft bearing failures on tow trucks due to lack of grounding on the bed mounted light bars. You have me intrigued as to why Jeep decided not to ground the frame (maybe cost and not needed). If I can find a factory wiring diagram I will look at it and see if it sheds any light on the subject.
I am late to the party but curious about this sentence “The way it is tucked in next to the mount on the 97, I'm not sure I would have always noticed it though.” - can you describe what you saw on your 1997? I have the same year but don’t recall any grounding wire or strap to the frame and starting to think that might contribute to my higher than desired SWR om my bumper / tire carrier combo mounted 2m radio antenna.
On my 97 there is a smaller gauged wire that connects from roughly this area of the frame to the oil dipstick stud.
The Goober question of the day has lasted nearly a year now.