Cab construction question (elec. ground)
 

Hello.

I will putting 50A Max sockets behind my seats and have a ground question.

How exactly is the cab grounded? The one place I know of is the bolt on the firewall where it is connected via a braided strap to the back right-side of the engine. But as far as the cab's construction goes, how is it assembled so the whole thing is grounded and at the same time not a rust-risk (if the cab is made of seperate pieces, the bare metal has to be connected electrically somehow)? For assembly/repair is the cab welded, then seam-sealed, then painted or something like that?

Below is the speaker corner where I would like to put a high-amp ground bolt. Will that work? (Yes, I'll be upgrading all my grounds)

Thank you.


Sincerely,
IM

Re: Cab construction question (elec. ground)
 

The cab is grounded via a braided cable to the engine and to the vehicle frame (the pickup box is also grounded to the frame).

The cab is comprised of separate pieces welded together and with seam sealer, as you have surmised, but because of the welding you have ground as if the cab was fabricated from one solid piece of metal.

Back then ground was achieved by shooting a bolt (with a star washer) through the paint, attaching the braided cable. You can imagine how that works out long term...

These days we use a copper weld stud attached to the sheet metal, which allows for an unpainted surface for continuity but without the corrosion concerns.

K

Re: Cab construction question (elec. ground)
 

Whoops, forgot to add that my truck is a 1981.

Re: Cab construction question (elec. ground)
 

This seem like a silly question, but how is it grounded to the frame? With the bolt that holds the cab to the frame? If so, isn't there a rust risk? (I'm a rust paranoid)


Thank you.

Re: Cab construction question (elec. ground)
 

The braided cable makes a more direct ground, not trusting the cab/body bolts. A similar technique is used to ground hoods and decklids (for radio interference protection), preferring a more direct ground and bypassing the hinge attaching bolts. In today's vehicles, with much higher electrical content (and much higher downside to poor grounds) the body is grounded to the chassis in multiple locations.

The whole "star washer"/breaking the paint idea was a terrible idea in terms of corrosion. That's how the taillamps on the stepside were grounded. The rust was so bad that every spring I would pull the tailgate, taillamps and brackets off and repaint them and reinstall. After I did that the turn signals didn't work - because I lost the ground. I ended up adding a short jumper wire from the bulb socket directly to the frame rail, which solved the problem.

I have the same problem on my open car trailer; I'd really like to ground to clean, bare metal but the problem is clean, bare metal rusts. The two requirements are at odds with one another.

K

Re: Cab construction question (elec. ground)
 

I just starting replicating new rear lamp harnesses and the harness on my 86 K10 has its tail light ground inside the LH tail lamp pocket on the inner box structure. All the grounds for the side markers and turn signal bulbs share this rather inadequate 16ga ground. On my own truck builds, I stud weld a 10mm stud to the rear frame and from there I run my rear bulb grounds as well as grounding the box too from underneath....so I retain the original tail lamp ground but with a 14ga wire and I run my grounds to my grounding stud on frame which then has a lead running to a floor brace of the box with a self grounding serraded machine screw.

Re: Cab construction question (elec. ground)
 

If it was me, I'd jump in with both feet.

Let's say worst case scenario you get a lousy connection with a 1V drop across it (which is a HUGE voltage drop across a connection), and by some miracle you're still pulling 50 amps through that spot. That results in 50 watts of power loss, 50 watts of heat.

50W in a transistor will have that sucker smoking within seconds, 50W of power loss in a transformer will melt the insulation of the wires. But 50W of power in a solid metal chassis with a surface area of a hundred square feet? Drop in the bucket. It'll create a warm spot, and nothing more. And that's worst case scenario.

So you build it, you test it. If the worst-case scenario comes true, you upgrade your ground path, maybe add a braided ground strap, and the problem disappears.

As long as you're grounding to the metal of the cab, I wouldn't hesitate even a little bit, because even if the rest of the ground path to frame and battery and engine block are all terrible, they're easy to fix.

Re: Cab construction question (elec. ground)
 

Your best bet is to add a true ground circuit. On my last build, I pulled everything under the hood and cleaned, sanded, and painted every part I removed. Even though I sanded every ground point to raw metal, I still had issues. I ran an extra ground wire from the battery to the block, and down to the frame. It was amazing how much better everything electrical worked.

Re: Cab construction question (elec. ground)
 

If you attach your bonding strap (ground) to a bare metal spot then seal it with a sealant that dries firm it can then be painted to prevent corrosion. The sealant will prevent paint from wicking under the attaching hardware thereby compromising the connection.