yep, speedo lamp, and an actual lamps current is needed to kick the alternator in at idle speeds.
A ~2500 rpm blip can also get it "exited" and kick in.
Addendum to Newtons first law:
zero vehicles on jackstands, square gets a fresh 090 and 1911, cabby gets a blower.
EZ3.6 Vanagon after that.(mounted, needs everything finished) then Creamsicle.
weldvair wrote:Can I run a wire from this terminal directy to the lamp in the speedometer?
Don
Yes.
the other side of the lamp has 12v on it: the lamp provides exciter current, will light up if you have no alt output.
I'm just noting It's not "just" an idiot light, it's an essential part of the circuit, and you cannot (directly) replace it with an LED for example.
(there are ways to use an LED if desired)
Addendum to Newtons first law:
zero vehicles on jackstands, square gets a fresh 090 and 1911, cabby gets a blower.
EZ3.6 Vanagon after that.(mounted, needs everything finished) then Creamsicle.
The wire held to the housing by the cheesehead screw is ground, and not really needed (it's a holddover from the earlier, externally-regulated, configuration that ensured proper regulator action). It can offer visual indication that the main ground strap around the trans mount has failed, though - if that little wire is melted, it's because it was trying to handle the job of passing all current between the drivetrain & chassis/battery.
Since the warning light serves that important function of providing field flash current and gives you an instant visual indication should the fan belt fail, I'd recommend that you find a place within your normal field of view to locate a lamp of some kind (preferably with an incandescent bulb for simplicity). Find a bulbholder assembly that uses twin leads (rather than the one-wire style which relies upon being mounted to panel ground). Wire one of the leads to the small terminal atop the alternator, and the other to a source of ignition-switched power. Many ACVWs came from the factory relying only on the use of very small-gauge wire which, in the event of a short, would burn up before the ignition switch - so follow that example and use 18 or 20GA if you come directly off the switch. Larger wire is fine if the power source is fused.
Quick question,
I understand that the Alt. needs to be excited with some sort of load, could that load be a voltmeter or does that not provide the same function? If you wanted to hook a voltmeter directly to the Alt how would that work?
The alternator gets its excitation current via the filament of the warning lamp bulb. Without that, it may or may not start charging after it's been parked for even a short time (unlike generators with steel housings and big permanent magnets inside, the alternator retains very little residual magnetism to get the party started)....so you really must have a lamp in that circuit, with the other side of it connected to the switched side of the ignition. Even a bulb in the engine compartment would do that job, simply wired to Term 15 of the coil - but that wouldn't do you any good as an indication of a tossed fanbelt, so put one on the dash somewhere you'll notice it.
The voltmeter can be hooked up anywhere in the system (but not to the D+ terminal) - however if you connect it to unswitched (B+ or Term 30) power it'll be drawing a tiny bit of current to keep it active 24/7 which might discharge the battery given a long enough time in the driveway. Not much to be gained by adding a dedicated wire from the engine compartment to the dash, either, and that has the potential liability of shorting out someday and wreaking havoc. I'd most likely choose to tap off one of the fuses that's only hot when the key is on, since there's really no need to be monitoring battery voltage when you aren't present.
TJ530 wrote:Quick question,
I understand that the Alt. needs to be excited with some sort of load, could that load be a voltmeter or does that not provide the same function? If you wanted to hook a voltmeter directly to the Alt how would that work?
No. Even if a voltmeter would pass enough current through it to excite the alternator (and it probably won't), as soon as the alternator starts working, the D+ terminal on the alternator goes from being ground to being +14V. That means both wires to your voltmeter are now at +14V and the gauge stops working. This is why the bulb turns off once the alternator is charging.
