Electric - "Alt Exciter" switch and light

[dbdevkc]

'50 Ford sedan - previous owner converted to 12v and installed wiring harness kit. The is a toggle switch and little LED light at the bottom of the dash. As long as the ignition switch is on, car running or not, if we switch that toggle the LED comes on. The wire going to that switch is labeled "Alt Exciter".

Any idea what that might be for? I thought maybe it was a charging indicator based on the wire name, but then why have it on a toggle...

[dbdevkc]

I found this:

"The exciter wire tells the alternator that the ignition is on and is the "turn-on" lead for the alternator. Power comes to that terminal from the battery, through the ignition switch. Once the alt starts charging, current reverses.

So, until the alt starts charging, battery voltage illuminates the bulb because there is no juice coming from the alternator. Once it starts charging, it generates an opposing voltage so that the net voltage across the light is very low (too low to illuminate it). The bulb is getting pushed about the same amount from both sides for a net near zero."

So then the questions are, why is the light on a toggle, and why is the light on even if the car is running - and we do know that the alternator is working and charging.

I guess we'll take a closer look to see where that alt exciter wire terminates.

[dbdevkc]

ok - finding a lot more info searching for "alt exciter" wire... But still I see no reason why there is a toggle switch on that wire. And something is going on why the light stays on when the car is running. Although we only switched it on just after starting while the engine was at idle.

[ford38v8]

As I understand, single wire alternators don’t begin to charge until RPMs increase beyond idle speed, and will then continue charging at idle also. If your indicator light stays on while driving, then I guess something else is going on, and perhaps the previous owner wanted to be sure to not drain the battery with the light while parked.

[34fordy]

I remember back years ago working on an old Jeep that someone had put in a later engine and went to 12 volt. For some reason in their rewiring, when the key was used to shut the engine off, the engine kept running. The alternator was feeding the ignition and the charging needed to be stopped. The cure was to turn the key past off position to accessory and then when the engine stopped turn back to off position. This was about 50 years go so it is bit fuzzy. Maybe it was a diode malfunction. I just do not remember. LOL

[5851a]

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I don't know if an led bulb would work as a warning light properly.

[big job]

sounds like (back when) you would buy a cheap indicator light being 12v #57 bulb then a wire from the Ign. Sw to any wire on the bulb and the other bulb wire to the F field (exciter) spade on the Alt. the other Alt spade a short wire to the + output terminal. my front end loader is that way Think its a common Delco (S1 ??) the bulb is just hanging there side the alternator been like that for 10 yrs works perfect. brain flash the power to the blulb I ran a wire from the + side of the coil. Also the second alt spade to the +output senses batt voltage. The bulb acts like a resistor and Napa told me to do it that way.

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[cadillac512]

On the 10SI Delco alternator, #2 on the plug is wired "hot" at all times and #1 is "hot" with the ignition on. The bulb (not an LED, they don't pass enough current...use a bulb the size of a dash light) is wired in series in the #1 wire. The bulb will light when the ign is turned on, and will go out when the engine starts and the alt begins charging. No extra switch is needed or recommended.

[34fordy]

Originally Posted by cadillac512

On the 10SI Delco alternator, #2 on the plug is wired "hot" at all times and #1 is "hot" with the ignition on. The bulb (not an LED, they don't pass enough current...use a bulb the size of a dash light) is wired in series in the #1 wire. The bulb will light when the ign is turned on, and will go out when the engine starts and the alt begins charging. No extra switch is needed or recommended.

Does the resistance in the bulb prevent enough current from flowing back to the switch to keep the engine running?

[rich b]

Originally Posted by 34fordy

Does the resistance in the bulb prevent enough current from flowing back to the switch to keep the engine running?

The bulb serves as a charge indicator and stops back feed when ignition switch is turned off.

A diode will work in place of the bulb to stop back feed if you don't want a charge light.

Exciter wire can also be connected to the accessory terminal of the ignition switch to separate it from the ignition and prevent feed back when ignition switch is turned off.

An LED will not work in place of a bulb.

Sounds like the original decided to use a toggle switch instead of wiring the alternator exciter via one of the normal methods.

This applies to a normal three wire integral regulator alternator.

None of this exciter wire business applies to a one wire alternator.

[Jack E/NJ]

>>>Does the resistance in the bulb prevent enough current from flowing back to the switch to keep the engine>>>


Yes, a 1/2 to 1 amp incandescent idiot light should pass enough current to properly excite the alternator but not enough backfeed current for the coil.


An LED light might not pass enough current to properly excite the alternator but won't provide any backfeed current for the coil just like an ordinary diode.

[dbdevkc]

Ok, so I might have been completely off base with "LED"... it is a regular bulb. But with a quick examination during a visit to where it is stored - it is a one wire alternator. When we have more time we'll need to trace out that wire because now having the toggle and light makes no sense at all. Perhaps the one wire alternator is a new addition? Or maybe there is some sort of other external regulator involved.

[Gene1949]

Originally Posted by cadillac512

On the 10SI Delco alternator, #2 on the plug is wired "hot" at all times and #1 is "hot" with the ignition on. The bulb (not an LED, they don't pass enough current...use a bulb the size of a dash light) is wired in series in the #1 wire. The bulb will light when the ign is turned on, and will go out when the engine starts and the alt begins charging. No extra switch is needed or recommended.

Same way I wired my 97 SVO Taurus alternator. The field wire is run in series with the bulb on the ignition side of the switch. THE #2 is a "sensing" wire. While it will work attached to the output that defeats the purpose. I've got the sensing wire off the Ford alternator wired to the battery side of the starter relay.
I've never figured out the fascination with "1 wire" alternators. With the smallest pully I could find the voltmeter shows 13-14 volts at 1000-1200 rpms with everything running

It would be interesting to understand what the previous owner had in mind.

[Jack E/NJ]

A 3-wire alternator can be easily converted to a 1-wire setup by simply leaving the alternator's exciter terminal disconnected. Then pig-tail a small wire from the alternator's sensor terminal directly to the alternator's main output terminal.


A 1-wire setup might require a small blip in engine rpm to get it to self-excite and start charging because it's no longer excited by the current via the ignition switch & bulb.

[5851a]

Originally Posted by Gene1949

Same way I wired my 97 SVO Taurus alternator. The field wire is run in series with the bulb on the ignition side of the switch. THE #2 is a "sensing" wire. While it will work attached to the output that defeats the purpose. I've got the sensing wire off the Ford alternator wired to the battery side of the starter relay.
I've never figured out the fascination with "1 wire" alternators. With the smallest pully I could find the voltmeter shows 13-14 volts at 1000-1200 rpms with everything running

It would be interesting to understand what the previous owner had in mind.

I agree never understanding the 1 wire fascination. If the 1 wire works fine in every case the factories could have saved a lot of money.

[34fordy]

Originally Posted by 5851a

I agree never understanding the 1 wire fascination. If the 1 wire works fine in every case the factories could have saved a lot of money.

I think they did save a lot of money by not having an amp gauge to show charge or discharge. Just the "idiot" light. LOL

[dbdevkc]

Well, here's news... That wire labeled alt exciter doesn't even run to firewall forward - it runs somewhere to the back and we haven't ripped enough apart to find it yet but it terminates somewhere behind the front see and in front of the trunk. To be continued...

[Gene1949]

Originally Posted by dbdevkc

Well, here's news... That wire labeled alt exciter doesn't even run to firewall forward - it runs somewhere to the back and we haven't ripped enough apart to find it yet but it terminates somewhere behind the front see and in front of the trunk. To be continued...

sounds like one of those guys who don't know how to wire an electric fuel pump

[dbdevkc]

They also have a wire to the trunk for an electric fuel pump, so that's not it.

[Jack E/NJ]

>>>That wire labeled alt exciter doesn't even run to firewall forward>>>


Check to see if a wire is connected to the alternator's exciter terminal. Then try to trace to its other end.