...Everything is stock other than the blower motor and wiper switch.
I'm going to go out on a limb here bannind and say that this is a false statement.
See below...;D
If I need to run another ground to the instrument cluster, I can do that as a 'precautionary' measure. Are the instrument cluster lights grounded via the instrument cluster housing?
Yes, the stock lights ground to the cluster housing through their little metal tabs/fingers that hold the lights into the housing. These are notoriously weak after this many years, so all the aftermarket replacement harnesses utilize separate ground circuits that bypass the socket entirely.
It's never a bad idea with an EB to run a jumper/ground wire from the little screw that holds the instrument voltage regulator (IVR) to the back of the housing. There are pictures hereabouts showing what this is, if you're not familiar with it. But it's also visible as being the only thing that is connected to all three gauges that use a sending unit (temp, press, and fuel).
Might as well inspect for rust on the housing surface, as well as for loose/weak connections between those tabs and the housing.
It is simply weird because my battery is located in the back of the bed passenger side. negative terminal is connected via a 3 foot 0 gauge cable to a mounting point on the top of frame.
This is most definitely NOT stock, so your wiring harness has been at least minimally invaded by the PO's of your truck (unless you did this conversion?) because the battery was originally in the passenger front corner of the engine compartment. You might know that already of course, but that was by way of stating the obvious that your wiring has been messed with.
The 0ga cable is great, but should run all the way to the engine for the best performance. However, if enough other grounds have been added things might be ok in that regard.
So where is the main engine ground? Are there any visible body grounds other than the metal-to-metal contact areas?
The entire cage of the bronco is welded into the frame at 8 different points with no rubber isolator pads (so the body is in good contact with the frame in multiple locations).
In general, what you say is correct, but age and rust and other factors of welding two pieces of metal together do not always amount to good grounding. What about paint? Is there paint on the body between the areas where the feet of the cage are bolted? Or is the cage welded to the body too? Should be bolted at least, and any welding would be strictly supplemental for attaching a body.
I would add ground straps in several places at the very least.
Where do I need to run another ground to on the instrument cluster? To be on the safe side I will run it all the way to the frame.
You should be able to run from the screw I mentioned earlier, to the body as long as you get the body bonded/grounded to the frame/battery better. No need to run it all the way to the frame, because I think you should ground the body to the frame in some different areas.
But don't let me talk you out of that completely, since making the extra effort to run ground wires and straps to the frame is not a bad thing. You just need to add some more connections to different spots on the frame and body to make it all work.
In my opinion anyway.
By the way, again, did you do this battery move or was it already done when you bought the Bronco?
If you have not already, remove the ground cable and clean/wire brush/etc the area around the bolt/stud or whatever is used to attach it to the frame.
Then do the same with the main engine ground up front.
If you're going to leave the frame as the main component in the grounding circuit, I would definitely add multiple jumpers to multiple parts of the body and cage. It's just cheap insurance...
You can use wire and eyelets you make yourself, or you can purchase some of the pre-made braided strap types that are sold at just about every auto parts store around. Use them to jumper/bypass the body mount locations between the frame, cage and body, in several locations from front to back. You don't have to do this to every spot of course, but don't rely on just one or two at one end of the truck. What we're fighting here is that after over 40 years of living together peacefully, the body panels are not in good contact with each other like they were when new. And this includes even those that are spot welded together.
A perfect example of this is the many stories about the front radiator core supports that are no longer grounded to the rest of the body. This makes the headlights dim and the turn signals work erratically. Even though those panels are spot welded together.
I have checked the fuse box and I am not getting juice into fuse #3 with the light switch activated. Does that call for a replacement light switch or is there another fuse in the chain that I need to check?
Should not be any secondary fuse in any of the stock circuits. Did you check for power there while spinning the headlight switch knob around? It might be a faulty rheostat in the switch, or it could be a loose wire or something like that.
What's the back of the fuse box look like? Is it clean, or all rusty and nasty?
Got pics of this rig of yours? Love to see under the hood and maybe even under the dash a bit to see what else might have been done to the wiring.
Thanks. And good luck.
Paul
