I recently converted my 57 Chevy from generator to a high amp 1 wire alternator, is there a way to keep the idiot light so it still comes on when key is in on position, but shuts off when car is running/ charging? I’ve heard people saying to connect to terminal 1 on alt, but my alt has power( with a test light ) at all times . It’s a supposedly self exciting 120amp alt The main reason I want to keep the light is just for nostalgic reasons of turning the key on and it going out once it’s started
too late, you should have asked before you bought the alternator. Most stock replacement alternators for 1975-1985ish Chevy 350s are 63 amp and have the 3 wires you want, so the light will work.
I know, but I needed a higher amp alt, running airbags & eventually a stereo system It’s not a big deal, but would like to keep the light if possible
This is what I found when I was looking at the same issue: Designing an "idiot light" (charge warning light) for a one-wire alternator is a bit different than a standard 3-wire setup. In a one-wire system, the alternator self-excites, meaning there isn't a dedicated terminal to trigger a light when the internal regulator fails. To make this work, we design a voltage-sensing circuit. The light will stay on when the battery voltage is low (engine off or alternator failed) and turn off once the voltage rises above a specific threshold (alternator charging). The Circuit Logic The Zener Diode: Acts as the "gatekeeper." It only allows current to p*** when the voltage exceeds its rated breakdown voltage. The Relay: Acts as the switch. We use the Normally Closed (NC) pin so the light is ON by default and only turns OFF when the relay is energized. The LED: Your visual indicator. Components Needed Zener Diode: 12V or 13V (1W rating recommended). Relay: Standard 12V automotive SPDT relay (5-pin). LED: Any standard 12V LED (or a 2V LED with a $470\Omega$ resistor). Resistor: A small 100 Ω resistor in series with the Zener to protect the relay coil. Wiring Schematic 1. The Trigger Side (Pin 85 & 86): Pin 86 (Coil Ground): Connect to the vehicle ch***is or battery negative. Pin 85 (Coil Positive): Connect the Zener Diode here. The cathode (side with the stripe) should face the power source, and the anode should face the relay. Power Source: Connect the other side of the Zener to a switched 12V source (Ignition ON). 2. The Light Side (Pin 30, 87a, and 87): Pin 30 (Common): Connect to a switched 12V source. Pin 87a (Normally Closed): Connect to the positive lead of your LED. LED Ground: Connect the negative lead of the LED to the ch***is. Pin 87 (Normally Open): Leave this empty. How It Works Engine Off / Ignition On: The battery sits at roughly 12.6V. This is below the Zener diode’s breakdown voltage (if using a 13V Zener). No current flows to the relay coil. The relay stays in the "Rest" position, completing the circuit through Pin 87a, and your LED shines. Engine Running / Charging: The one-wire alternator kicks in and raises system voltage to 14.2V - 14.6V. This exceeds the Zener's threshold. Current flows through the Zener, energizing the relay coil. The Switch: The relay clicks, moving the internal contact from Pin 87a to Pin 87. This breaks the circuit to your LED, and the light goes out, signaling that you are charging. Choosing your Zener Zener Rating Behavior 12V Zener Light turns off very easily, perhaps even on a very strong rested battery. 13V Zener Recommended. Provides a clear distinction between a resting battery and an active alternator. Note: Because automotive voltages can be "noisy," you might notice the relay chattering right at the threshold. Adding a small capacitor (e.g., 10uF) across the relay coil pins (85 and 86) can smooth this out.
heh...I thought about what it would take to do that, and didn't want to design it! Since I don't do bags or stereos or electric fans or whatever, the lowest output alternator is always enough for me. thanks for the write up!
You could wire the light to the ignition switch so its on when the switch is on. Run the fused light feed through a normally closed oil pressure switch. Turn key, light is on, engine starts, oil pressure turns the light off.
If you bought a powermaster the instructions show how to do it using the stock wires and using your old regulator as a junction point!
lil c, just run it . I have been running mine, a rebuilt from O'REILLY, for 14 years and 30,000+ miles. Ben
@Casual 6 , thanks for the write up on the work-around, but I think the price of resistor is off, can you please verify? $100?
The $ signs should be "Ohms", I think there is an Omega sign on this computer thing, but I couldn't find it either. And they would only need to be 1/2 watt.
In Windows it should be on the Character Map; it is on mine. I need to copy-paste it because I don't have a keyboard shortcut for it. 100Ω
THAT IS PERFECT ! thank you !!!!! LS-11 Lo Voltage Sensor, Factory Five Wiring Harness: Ron Francis Wiring
PERFECT, THANK YOU ! edit, ok, idiot light will not come on when key on (but not running) unless it drops to 11 volts or bellow.
That description of the parts and circuit should be in a Best Of section. You know this is going to be asked again. @lilCowboy do you have a voltmeter in the gauges? I have seen many aftermarket digital gauges in various videos and always wonder why they are so clunky. For each item displayed, they should have a programmable colored background. In this instance Voltage. When key on, it should be boring Gray background when 12 to 13 volts, Yellow when 10 to 12, and Red when under 10 or over 13. Same for all other parameters. Once the cluster receives an RPM signal of typical idle or more, these raise to indicate expected charging voltage. It's all just software.
Dumb word processor - couldn't translate the alternate characters correctly. Should be 100Ω for the resistor and 10uF for the capacitor. Edited and corrections made. Thanks for catching that.
Here's just some of the handy special symbols you can access using Windows Character Map (search "char map" in the Windows taskbar). ¢, £, ©, ®, µ, ¼, °, ±, €, etc.
The Jalopy Journal
