Alternator issue (1987 Bronco 2 actually )

I have an interesting issue, I put in the new alternator; this type has 2 sockets as seen in photo 1. Now, the two big black wires from the lower plug actually merge into 1 wire a few inches on the engine harness. The white wire plugs into the engine harness and loops directly back to 1 of the tabs on the upper socket. With engine running the alt does not charge the battery.
The battery stays at 12 volts, but I accidently touched a bare spot on the white wire to a bare spot of the black wire and instantly, the voltmeter hooked up to the battery went to 14 volts! It will stay charging as long at the engine is running (like normal).                       Shut down the engine, re-start and the voltmeter stays at 12v again (no charging) but quickly touch the white to black again (and release) and the alt "excites" and charges to 14 Volts. what is the problem? any ideas of what to check?

This is a 2G alternator? (sorry I'm not familiar with the Bronco II)

At the rectangular plug you should have two 10G bk/or wires that splice to a single fuse link and a W/B stator wire.
The regulator plug should have yellow (sense) green/red (excite, ignition on) and typically the W/B stator wire, but Gary has documented cases where there are only 2 wires at the regulator.

In any case, verify that the green wire is power in run. On trucks with idiot lights if the battery/charge warning light burns out the truck will not charge, until 'something' energizes the stator, but once charging it will bootstrap itself.

Honestly the 2G is a hazard.
There are good reasons for the TSB's about these starting fires.

Gary has them well documented in the 3G upgrade tab at the top of the page.

Thank you

I hope it's as simple as a fuse or the bulb in the green wire circuit.

When you turn the key on electricity flows through the filament, and when the alternator starts charging both ends are at the same potential, so the bulb goes out.

Again, I don't exactly know the Little Bronco, but that's how it is in pickups/FSB and Crown Vic s, Cougars, T-bird's and Lincoln MK's of that 2G era.

That make sense, now. The P.O gutted the interior to start "rebulbing" it. The instrument cluster, along with everything else has been removed so all the idiot light bulbs have been removed. He did say (and you can see it) when he pulled the cluster, a section of the printed circuit board "toasted". New cluster will be here today. Ill get it in and see what happens (with a fire extinguisher nearby)

Thank You
Reamer

By 87, the charge indicator bulb holder *should* have a 512ohm resistor bridge across the back of it.

I must Thank you on your pin-point solution to the issue, With the P.O. removing the instrument cluster, the Alt had no signal. As you said, the resistor was needed, I plugged in the cluster, and it is charging like a champ.
THANK YOU.....I could chase the for years!

Reamer

I'm 'glad" that I'm familiar with the 2G alternator.

But even more glad that it wasn't anything major, and a simple fix for you!