The Stovebolt Site Forums The Shop Area The Electrical Bay Interally Regulated Alternator Wiring Questions

Hi everyone. Got a couple of questions.
I have a 61 C10 and the generator was changed to an internally regulated alternator at some point. There is a toggle switch mounted on the dash that connects to constant 12V at the fuse panel. Other side of switch is spliced in to the small wire going to/from the alternator. The switch manually toggles when ignition switch is keyed on or off to keep the gen light off. Make sense?

My questions are:
Why does a switch need to be placed like that?
Will a new wiring harness enable me to get rid of the switch?
Are there wiring harnesses available for generator to alternator change outs that don't have the additional wires required for a external regulator?

As I dive in to this old girl I'm sure there will be more questions.

Thanks

Discovered that the switch was installed to place 12V onto the wire between the idiot light and alternator to excite the alternator. Question now is why?

It may be wired such that when you turn the engine off, it will continue to run until you turn the toggle switch off. You need to put a diode in the line to kill the power to the alt when you turn the engine off. Or you can buy a plug in from one of the many suppliers that does the electrical magic for you.

Tommy,
Engine shuts off fine regardless of switch position. It's just that the alternator won't energize until battery voltage is injected into the wiring harness near #1 alternator terminal. For some reason the ignition switch voltage passing thru the warning light is not enough to energize the alternator. Don't know why.

Get a voltmeter and check the wires that were connected to the old generator for 12 volts when ignition is on, no voltage when off. Use that wire for the alt. connection

Using the original wire on the alternator side of the warning light to get to #1 terminal on the alternator. Which I believe is the correct way to do it. For some reason I'm only getting 7 volts to Field terminal (#1) which is not enough to excite the alternator. Don't know where the 5 volt drop is coming from as the wiring is good back to the warning light. Could the warning light be dropping that much voltage?

This diagram and explanation is the best I've found. Scroll down one post. Get rid of that switch and wire it this way. Normally the light will come on as it starts and fades away as it generates. Having to switch it off means it's wired wrong. He shows how to jump the old regulator connector. If your connector is gone, just be sure the circuit paths are per diagram. If your truck still has the sensing wire, it is a funky looking wire/insulation and slightly larger in appearance. Sometimes it is looped back on itself to create a longer wire. The actual length is calculated for correct function. As he says, you don't have to have it but the light won't signal.
Click

Yup. That is the way it's wired up with the exception of the manually switched 12 volts tied in to #1 alternator wire to excite the alternator at start up. Has anybody ever measured the voltage at #1 with ignition switch on? I'm getting just a little over 7 volts which I'm assuming is not enough to excite the alternator. This problem must be very rare. Don't have many folks chiming in. Frustrated.

I always measure may voltage at battery with motor running. If it reads 14V or more, then I'm exited. Start you motor, put multimeter on DC 20, touch batt pos to pos and neg to neg and read output. If system is wired correctly and meter reads 14V +/- 1V, you should be OK.

Ideally, Pin 1 should read 12V when motor running, this provides 12V to both sides of bulb and it will not light. If Alt is not charging, Pin 1 will be grounded within alt and will light the light. Reading of 7V should be a dim light and you should also get a low reading at batt. Causes: Low idle, loose belt, bad alternator, alt not grounded thru brackets, system wiring wrong.....bad battery? Do not test Pin 1 with meter ground lead on alt. Touch batt neg.

Alternator is wired in correctly. It just won't excite when the truck starts. Picture a toggle switch with one lead connected to 12 V at the fuse panel and the other lead connected to the Field lead (#1) near the alternator. The field lead insulation was stripped back and the 12 V wire from the switch was connected there. The alternator will only turn on when the additional 12 V is applied from the toggle switch. For some reason the 12V from the ignition thru the warning light is not enough to turn on the alternator. Could the warning lamp be dropping too much voltage to keep the alternator from turning on?

You say you looked at my link and you said "yup it's wired that way except".....(no exceptions). If you want help, and you want to figure out what is wrong, try to follow instructions I gave you about measuring and report results or I can not help you. If you look at the link, #1 IS NOT the field lead. Wire it like the diagram I gave you, take out the switch. Wire one side of bulb to ignition "ON", wire the other side as shown in the diagram and wire the rest per diagram. Forget trying to analyze what is or is not happening until you wire it correctly and measure voltage, while running, AT THE BATTERY with a multimeter. If you want to keep explaining it to me some other way and why it's not working, you are just blogging and wasting time. While you are at it, take out the bulb and test it to be sure it is working. The system should have a resistance wire in parallel with the bulb so that a bad bulb will not keep alternator from charging. Why have you not said what the voltage is at the battery when truck is running?????
C'mon Mike, work with me here. Trace all your wires and be sure it is per diagram. Be sure you are reading the diagram instructions carefully. The numbers will fool you. There is 1 or I(as in Indicator, as in Indicator bulb) and 2 or F(as in Field, as in voltage sensing) on alternator and there is 1, 2, 3 and F on the old regulator connector, which you may not have anymore. So you have to understand the circuit flow, without that connector, and be sure you are wired that way.
You are talking about "excite", "voltage drop" "field lead" and checking #1 output, forget all that and wire it carefully per diagram and don't worry about the "buzz" words yet.

Your alternator is not wired correctly if it has an extra wire cobbed in to give 12V to the #1 terminal. That terminal does not need voltage input for the alternator to operate properly. Terminal #2 is the sensing terminal. It needs input voltage to start the alternator charging.

As explained above, #1 terminal operates the light. When you turn on the key, 12V is sent to the light circuit and it finds a ground in the alternator. When the alternator is charging there is 12V at terminal #1. Therefore, the light can find no ground and can not light.

Also you state it is wired just like the diagram Bartamos linked to above. That diagram is for conversion from an externally regulated alternator to an internally regulated one. If your truck originally had a generator it will not have the plug shown in that diagram and can't be wired that way.

I'd suggest that whoever wired this had no idea what he was doing. I'd also suggest finding someone who does know what he's doing to re-wire it.

I agree with Cletis, but try one more time. The truck does not know it ever had a generator. You have all the components shown in the diagram: you have a "Gen Light", you have a dashboard, an internally regulated alt, a starter solenoid and you do have a battery. Just wire per diagram circuit in link. Ignore the regulator connector, as Cletis indicates , you never had that type regulator, but that does not matter. Just notice how the circuit flows. Forget note 5. Read and understand note 6. The diagram should have shown a line coming out of the box marked "To indicator light on dash" and going to IGN switch 'On".

FYI: Some diagrams show one side of bulb to "switch". The PO thought this meant he had to add a switch. The "switch" mentioned is the Ignition switch.

If you don't care about a light and you don't care about sensing, Note 6 provides a simplified hook up.

This could be confusing to poster. I have said several times to wire it that way, ignore the connector (plug), but copy the circuit.

Per your diagram:

Switch is out of the #1 circuit. No longer a player.

Alt output terminal is connected to battery. Check

#1 or Indicator terminal is connected to red lead from firewall plug which goes to indicator light. Check

# 2 or Field terminal is connected to battery at Alt output terminal. Check

Truck running:
Indicator light is ON
Battery voltage is 12.54 V

That is the voltage of a battery at rest and fully charged. If truck is running and that's all there is, Bad ground to alt, loose belt, bad alt....and the light on when running supports that. Take alt to O'Reilly's, Autozone or equivalent to get tested for free. That is your next step. Thanks for the update Mike.
I realize you are pretty rural. Hope there is some place closer than Concordia to test. It's good to go to a testing place that you are sure has the alternator in stock, so you only make one trip. If you are sure it's all good and grounded and spinning, it is probably bad, but I, myself, don't trust myself, so I need someone that tests it outside of truck, away from any mistakes or bad issues. But I don't live 15 miles from O'Reillys either. Maybe just try it with a one wire setup. Batt hot to alt hot. Heavy gauge wire (10 or 8 ga)

10-4.
Thanks.

Mike I was still typing , reread.

Thanks, but I want to stay with the three wire for better regulation. I plan on moving the sense wire downstream. The electrical doesn't look too bad in the truck(other than the "Bubba" job to get the alternator to turn on). I will replace the generator harness from the firewall with a new alternator harness just to clean things up.

I just meant try that before taking to tester, not permanent.

What is the specification for the diode to install in the wire from the ignition to terminal #1 of the 10Si? I have a '55 235 powered truck that will start, run and charge; but will not shut off with the ignition key switch.

Try a 1N5285 diode. Lots of them on Ebay at about $2.00 apiece.
Jerry

Jerry - I was able to find that diode at a local shop that builds circuit boards. One in place, truck shuts off with key now. Thanks for the hint.