Ground to frame or body

[flynylon]

I've got good ground to the engine, but where does the engine ground to the frame? I may be missing something, but I can't find a ground wire between the engine and the frame.

Thanks!
mike

 

[Viperwolf1]

They didn't come with one but it's a real good thing to add. The only stock device that grounds to the frame is the rear tank sender. I guess Ford figured the current was small enough for that to get through the body mounts and u-joints without much problem.

I added a stud to the frame under the battery. My engine ground goes there as well as the battery neg, a strap to the inner fender and a radiator ground. I'm using a frame-grounded winch so I need all the current I can get through there.

 

[DirtDonk]

Another real easy one is the wire or store-bought braided strap from the back of the intake manifold to the firewall. Pretty much all modern vehicles have had them since the seventies, but Broncos didn't seem to rate.
The original ground cable from Ford had a section that attached to the inner wall of the fender well. You can probably still see the hole where the sheet-metal screw held it down.

Like Viper was saying, you pretty much can't add too many grounds on a Bronco. Even the parts that were originally grounded have long since seen their good clean connections go away. Rust, corrosion, dented panels, separated welds, and whatever else, conspire to isolate important things like the core support (headlights and running lights), the dash board (instrument cluster and all sorts of little thingies), the frame (fuel tank, and the steering column (horn and probably other things too).
So you just can't have too many ground wires running hither-and-yon to re-connect different body and chassis parts.

Have fun!

Paul

 

[flynylon]

I am thinking that herein lies the problem. I am trying to isolate a dead fuel gauge issue. A couple weeks ago, both sending units were working. I just replaced the rear one with a Carpenter repro unit about six months ago, and while both went to empty way sooner than either tank ran dry, I was pretty happy that they functioned.

A couple weeks ago, the gauge went zero for both tanks. I have continuity on both positions on the switch, and I can power the gauge to full with a 9-volt battery. I've cleaned the ground on both pigtails, but I still get nothing on the gauge. The strange thing is that I switched over to the Aux tank with the manual selector a couple days ago, and the gauge suddenly started working for a little while for both tanks, and then it went back to zero.

I figure it must be a bad ground on the chassis, but I can't figure out where the issue is even after running a 14 ga wire from the battery to the body. Everything else works, but the gauge still doesn't.

I really appreciate your thoughts and input.
mike

 

[DirtDonk]

Tak another wire then and run it directly to the frame. Remember that the body is isolated from the frame by all that rubber or polyurethane, with very few places for the electrons to pass.

Can't hurt anyway.

Oh, and how do the water and oil gauges read?

Paul

 

[flynylon]

Paul, I think a weak ground to the chassis must be the issue, but I can't even guess why the engineers at FoMoCo didn't tie the engine to the body/chassis in a more positive way (excuse the pun). Let me try a braided strap or four and see if this issue goes away.

Thanks y'all!!!
mike

 

[flynylon]

My ammeter bounces a lot, but the oil pressure and temp are both steady.

 

[DirtDonk]

Yeah, they certainly left out even the things that cars of that day and age were using. Even the pickups were getting more love. My '79 has a strap between the engine and firewall, the hood and cowl, two clamped between the cab and frame, and probably more that I'm not remembering.
Guess they were either gettin' it all figured out at that point, or just got the approval from the committee of money-watchers that it was ok to spend 35 cents extra per million vehicles sold, in order to avoid the inevitable complaints when things started to fail to work after a few years.

Or something to that effect.
Good luck with yours. Plenty of people here with issues regarding their fuel sending units and gauges, but it never seems to be just one thing. Instead it's 30 years worth of little things added up.

Reason I asked about the other gauges is that one of the weak areas of current flow is the dash ground, the instrument cluster's deteriorating connection with said dash, and the IVR on the back of the cluster losing it's battle with rust between it and the body of the cluster.
If all of your gauges (except for the ammeter of course) were reading a bit low, and if your dash lights are NTU (next to useless) then a new dash grounding scheme might be in your near future as well.

Paul

 

[DirtDonk]

Ammeter bouncing is usually one of two things (but could be others probably too). Either your main voltage regulator is slightly whacky, or your gauge is getting a bit old.
Then again, maybe we can go back to that bad grounding scheme? Not sure how grounding would, or would not, effect the ammeter. It's on it's own, while the other three gauges work by means of a pulsing voltage signal through the IVR (instrument voltage regulator), also called a "constant voltage supply" for some reason.

Paul

 

[flynylon]

Could the IVR have shit the bed and caused the sending units to peter out?

 

[DirtDonk]

Hmmm, don't think so, but I'm not 100% sure about that. Just guessing.
I think the sending units are pretty robust from a slight over-voltage standpoint. They're not robust in many other ways, but don't think 12 volts would hurt them.

Have you ohmed-out the sending units? Might as well make sure you're getting the required 15 to 73 ohms, or whatever it's supposed to be. Others will know. 40 years of dealing with them and I still can't remember the different resistance values for a simple sending unit, ignition coil, or distributor trigger.
You'd think after all this time... But noooooooooooooooooo. ;D

Paul

 

[flynylon]

Both sending units worked a couple weeks ago, and then the gauge went dead all of the sudden. The only exception was when I manually switched tanks, and I got values out of both tanks for a little while. Then they both went back to zero.

I really appreciate your help on this one. I am perplexed, but the ground thing makes sense.

 

[DirtDonk]

Well, at least the good side to all this is that, even if it's not the cure, adding all these new grounds can't but help everything you do in the future.
And it eliminates one possible culprit.

I would perhaps connect the main tank directly to the gauge too. I know you said you checked the switch, and it seemed to be working properly, but they are notorious wear items and can act inconsistent for years, before failing completely.
Under the dash you should be able to follow the orange wire near the switch area, that will have a little 90° plug somewhere. The other end of that goes to the switch. But there is another one AFTER the switch that matches it. Simply pull the two apart and join them without the switch in-between.
It's basically the layout you'd have if you didn't have the optional AUX tank.

Eliminating and isolating things for free first, is always a good method. THEN spend money if you have to.

Paul

 

[HoosierDaddy]

I am thinking that herein lies the problem. I am trying to isolate a dead fuel gauge issue. A couple weeks ago, both sending units were working. I just replaced the rear one with a Carpenter repro unit about six months ago, and while both went to empty way sooner than either tank ran dry, I was pretty happy that they functioned.

A couple weeks ago, the gauge went zero for both tanks. I have continuity on both positions on the switch, and I can power the gauge to full with a 9-volt battery. I've cleaned the ground on both pigtails, but I still get nothing on the gauge. The strange thing is that I switched over to the Aux tank with the manual selector a couple days ago, and the gauge suddenly started working for a little while for both tanks, and then it went back to zero.

I figure it must be a bad ground on the chassis, but I can't figure out where the issue is even after running a 14 ga wire from the battery to the body. Everything else works, but the gauge still doesn't.

I really appreciate your thoughts and input.
mike

My issue was/is in the ignition key switch. Every now and again I'll be driving along and get a good scare when I look at the fuel gauge and it is EMPTY . Jiggle the key a bit and the fuel gauge starts working again.
I think the key is stopping between two different positions , which apparently holds certain circuits open.