My dash light has never been correct. It turns on when the ignition is on and engine is off. When I start the engine, the light stays on. I have a 1UZ engine, and the alternator has the 3 pin socket. In the diagram below L is the ground coming from the LED dash light. If I wire it like the diagram the alternator won't work. L and IGN have to be swapped. S is also 12v. My understanding is the LED light grounds out through the alternator. When the alternator is on, it sends 14v thru L, which is no longer a ground, and the light turns off. But this doesn't seem to be the way it works.
Alternator dash light question
- Thread starter Pow3r
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Ken Roberts
Supporter
I think your problem is the fact it's a LED bulb. It's supposed to see the resistance of an incandescent bulb.
I did some more looking and yes the alternator needs to see the load from an incandescent bulb to get the field coil energized. The LED isn't enough to do that. This has been discussed a lot, and for those insistent on using an LED, some have suggested you can run a 50 ohm resistor in parallel with the LED, like this:
I set that up on a project board and that didn't work. The LED light wouldn't illuminate. Reading the description closer, it needs to be a shunt resistor: 50 ohm and 5W. I couldn't find anything that seemed to match that description online, and realized there may be other resistor names like current sense resistor and cement resistor that might be the same thing? I got lost in choices and decided to go for the simple solution. Just use an incandescent bulb. But the bulb wouldn't illuminate using the wire back to the alternator as the ground. Oddly enough, the LED warning light would illuminate. I ran a fresh 12v wire straight from the fuse box, and the incandescent light works with a regular ground but won't illuminate using the alternator ground (with the 3 terminal socket wired according to the initial diagram I first posted).
So to summarize: the alternator works if I swap IGN and L according to the diagram. But the LED dash light stays illuminated when driving. If I put IGN and L in the positions according to the diagram, the alternator doesn't work, and the dash light is always on. Am I missing something simple?
I set that up on a project board and that didn't work. The LED light wouldn't illuminate. Reading the description closer, it needs to be a shunt resistor: 50 ohm and 5W. I couldn't find anything that seemed to match that description online, and realized there may be other resistor names like current sense resistor and cement resistor that might be the same thing? I got lost in choices and decided to go for the simple solution. Just use an incandescent bulb. But the bulb wouldn't illuminate using the wire back to the alternator as the ground. Oddly enough, the LED warning light would illuminate. I ran a fresh 12v wire straight from the fuse box, and the incandescent light works with a regular ground but won't illuminate using the alternator ground (with the 3 terminal socket wired according to the initial diagram I first posted).
So to summarize: the alternator works if I swap IGN and L according to the diagram. But the LED dash light stays illuminated when driving. If I put IGN and L in the positions according to the diagram, the alternator doesn't work, and the dash light is always on. Am I missing something simple?
Ken Roberts
Supporter
CHECK THE PINOUTS (on the connector).
pin#1 should be L.- Connects from 12v ignition to indicator lamp and then to terminal "L" on alternator.
pin#2 should be IGN.- Connects from 12v ignition to terminal "IGN" on alternator.
pin#3 should be S.- Connects from Battery to terminal "S" on alternator.
NOTE-Usually pin#3 is referred to as the sense wire. It is important to connect it at the point where all the main circuits are drawn from (usually the starter motor on production cars). Never connect in a short loop back to the alternator output. This defeats the purpose of it. Its job is to sense the actual voltage of the system at the distribution point. Then it adjusts the alternator regulator output to compensate for the voltage drop in the wiring.
pin#1 should be L.- Connects from 12v ignition to indicator lamp and then to terminal "L" on alternator.
pin#2 should be IGN.- Connects from 12v ignition to terminal "IGN" on alternator.
pin#3 should be S.- Connects from Battery to terminal "S" on alternator.
NOTE-Usually pin#3 is referred to as the sense wire. It is important to connect it at the point where all the main circuits are drawn from (usually the starter motor on production cars). Never connect in a short loop back to the alternator output. This defeats the purpose of it. Its job is to sense the actual voltage of the system at the distribution point. Then it adjusts the alternator regulator output to compensate for the voltage drop in the wiring.
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John
Lifetime Supporter
If you do the math, 5W seems overkill but if you want to try one, you can order one here: https://www.mouser.com/ProductDetail/Vishay-Dale/CMF5550R000FKEK70?qs=epEKMuKXWIISYoq8AMijSg==
Thanks for the reply, are you saying pin 1 is the lower right and pin 3 is the upper terminal, same arrangement as in the diagram I showed? I don't have S going to the starter/battery. I'll change that, but it shouldn't affect why the incandescent light won't illuminate with ignition on/engine off...?
John thanks for the link. Is that resistor different than resistors available on Amazon? I have an assortment, 47 ohm 1/4 watt vs 50 ohm 1/2 watt in the link. Is that an appreciable difference?
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Ken Roberts
Supporter
The PIN numbers should be written on the connector shell.
There are no numbers on the connector to identify pin 1.
Using female spade terminals I connected the battery to S on the alternator, a wire from the switched fuse panel ran to an incandescent 5W bulb and the other wire of the bulb to L on the alternator. I put a male spade connector in the IGN pin and of the socket and ran it to the IGN on the alternator. I powered the ignition, and the light didn't illuminate. The terminals at the bulb show 0 volts, and the L wire going to the alternator is not grounded. I checked for ground on the other two wires coming from the alternator, neither show ground. With the incandescent light still connected, I connected the LED in parallel with the incandescent bulb, nothing worked. If I unplug the incandescent bulb, the LED comes on. I start the motor, and the LED won't shut off. And the alternator isn't charging. I unplug the LED and plug in the incandescent bulb and the engine idle lowers slightly. I checked the voltage and the alternator was charging.
I don't understand what's going on.
Using female spade terminals I connected the battery to S on the alternator, a wire from the switched fuse panel ran to an incandescent 5W bulb and the other wire of the bulb to L on the alternator. I put a male spade connector in the IGN pin and of the socket and ran it to the IGN on the alternator. I powered the ignition, and the light didn't illuminate. The terminals at the bulb show 0 volts, and the L wire going to the alternator is not grounded. I checked for ground on the other two wires coming from the alternator, neither show ground. With the incandescent light still connected, I connected the LED in parallel with the incandescent bulb, nothing worked. If I unplug the incandescent bulb, the LED comes on. I start the motor, and the LED won't shut off. And the alternator isn't charging. I unplug the LED and plug in the incandescent bulb and the engine idle lowers slightly. I checked the voltage and the alternator was charging.
I don't understand what's going on.
