Here's a pic of what the Starter relay and Junction block look like today after a total restoration. I believe I have all the connections correct except I think I might be missing 1 wire as I may have purchased the incorrect alternator harness from CJ pony parts.
Or they only have the incorrect harness.
It's possible that even though someone lists a '66 harness now, it might fit only the later build models that appear more like the later Broncos.
My central question is: Should there be a wire connecting the BAT terminal on the alternator to the Junction block?
Only if it's there simply as a junction block, and that the other wire connected there runs up into the firewall to function as it does on later models.
(This would mean 2 wires going to the BAT terminal.) One from the short alternator harness and two; the "jumper" from the BAT terminal to the junction block.
No, not needed. No reason for Ford to have used two because it would cost more money and be unecessary.
What is this "short" alternator harness? The one from the back of the alternator to the 3-wire plug/connector?
It is impossible to find a wiring diagram that includes this junction block and it's connections.
Common issue with first year vehicles and when the OE manufacturer was making running changes as early production progressed.
This is especially common when small electrical wiring changes were made. All the books from Haynes and Chiltons (and possibly even Ford) from the early days until now have missing aspects.
First is as you've found, nobody lists the differences in '66 early or late or through the entire run. They lump '66 to '71 in the same diagrams. So that means that for '71 they are wrong also.
Ford made major changes to the entire harness between '70 and '71, yet the diagrams all lump '71 into the same early design.
Pickup trucks too, where the books show the wrong fuse panel. Sometime between '75 and '76 Ford went from the same 5-fuse panel that we have on our Broncos to the larger 10-fuse panel. But they continue to list the 5-fuse panel all the way through '77.
Makes things very confuzzling sometimes until you have time to drill down to find the discrepancies.
As you can see from the original photo there are two large (#12-#10) wires going to the junction block. I just don't know where the other end of that solid black wire goes...
Then most likely we don't either. We can make suggestions, but only you have the vehicle and can physically trace the wires.
You can do this by testing with the ohm-meter or by physically tracing the wire through it's entire run.
Seems to me that the junction block addition might have been due to what Viperwolf said in the other thread, that they were adapting an alternator harness from another vehicle and this terminal block was the simple and quick production line fix for the problem that was not noted by the designers.
Or was a result of the correct Bronco harness not being available when production started, so someone just used what they had and made a workaround for it.
But when I first saw that I figured (perhaps correctly, perhaps not) that one Black w/yellow wire ran from the BAT terminal on the back of the alternator over to the terminal block and the second one was your main charge loop wire that ran up to the firewall.
This makes the most sense to me at least at the moment.
The truck has an ammeter gauge. (Not and idiot light).
Yep, that's at least one thing that has been consistent from the first to the last Bronco built that we know of. Never a light, just the ammeter in every one.
The large Black/Yellow wire to the junction block is one end of the long loop that runs thru the back of the ammeter gauge.
This is perfect. In theory the only two wires to that terminal would be this one from the ammeter and the short one from the BAT terminal of the alt.
The other end of the black/Yellow wire is the large solid Black wire connected behind he Red Positive Battery cable on the starter relay.
This is correct and is how literally everything works on a Bronco.
As mentioned before, when the alternator is not working then everything gets it's power from the battery via this wire.
When the alternator is working and is putting out more than the battery is (12.6v at the battery vs 14.5v from the alternator) the alternator powers everything and charges the battery at the same time, via this wire.
What appears to be missing is the other large wire to the Junction block. I'm guessing that if there was a wire going from the junction block to the BAT terminal on the alternator this would complete the circuit allowing the alternator to charge the battery?? Thanks for the continued help!!! Damn 66's!!
Yep, you got it exactly.
So the question is, where does the current Black wire from the BAT terminal go now?
This is the question about the harness and the main connector it sounds like. As you surmised, the new harness is not the same as your old one. Is the rest of the vehicle harness original, or is it a brand new '66 harness?
So no, it sounds like you do not need two BAT wires. But yes, it sounds like you need two of the Black wires on the terminal block or nothing is going to function regarding the charging of the battery.
Got more pictures? A wider shot at least? We need more pics please.
Show the regulator and it's plug. Show the back of the alternator if you have access to that.
Thanks
Paul
