Why is it that since the advent of the OBD system have instrument clusters needed to be plugged in to have a proper alternator charge? I'm in the processing of eliminating the hoards of unnecessary chassis harness from my chumpcar and this baffles me that it's such an integral part of the car running to have the cluster plugged in on all newer cars.
Pic of some of the wires i've deleted.
It's not just since the advent of OBD systems. The "alternator" light has been part of the charging circuit for decades and decades. Possibly since alternators started being installed in cars. I don't know the details behind it off hand, but basically the bulb has to be there and intact (functioning) to allow the alternator to power the coils.
dculberson wrote: It's not just since the advent of OBD systems. The "alternator" light has been part of the charging circuit for decades and decades. Possibly since alternators started being installed in cars. I don't know the details behind it off hand, but basically the bulb has to be there and intact (functioning) to allow the alternator to power the coils.
I did not know that. I thought it came with OBD systems. Thank you
Now with that being said - does anyone know how to bypass the system on a 1994 Honda Accord haha?
Connect a 12v bulb to the alternator warning lamp terminal on the alternator like this:
Random pic pulled from the internet so I can't claim responsibility or credit.
The warning light wire tells the alternator to "turn on." Find this wire going to the alternator, and put 12v+ to it. Or, simply put in another light so that you know if your alternator is charging. Put 12v+ to one side of the light, and run the other side to the alternator. When the alt isn't charging that circuit goes to ground, light turns on. When it's charging it puts out 12v+, light turns off.
The exception of course would be a self-exciting alternator, like an old GM 1-wire.
Hey, I'm like a GM alternator! 
Thank you gentlemen
All alternators have a 'field winding' which is just a coil of wire that creates a magnetic field when current is passed through it. On any alternator, if you are able to get to and connect to the two ends of this wire, you can hook up a $17 external voltage regulator and make the thing work. It's just that on some alternators, the two ends of this wire are not easily accessible or obvious as to what they are.
dculberson wrote: Connect a 12v bulb to the alternator warning lamp terminal on the alternator like this:
I was just watching a South Main Auto Repair video on Youtube the other day where someone had added a light bulb in the wiring harness under the hood, right next to the alternator, to bypass the dashboard cluster.
I've said it before and I'll say it again, put a switch that goes open between the light and the alternator when you get to WOT.
Then you will have a few extra hp since the alternator isn't charging, but you will also have a dashboard light reminding you how awesome you are.
Note, this might not be a great idea in an endurance racer that spends a great deal of time at WOT.
I have a VW and that had a charging issue. I had the alt. tested and they said it was OK but it wouldn't charge the battery! I finally figured out that the circuit running from the alt. to the "little light in the dash" was dead. When I ran a new wire from the ign. switch to the "trigger wire" of the alt. with a small 12V bulb in line it started to charge fine!
Got it bypassed tonight. Thanks for the help. Cut another few precious ounces of weight out of the car.
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