Quote:
Originally Posted by memo43
bhap
I'll try running both (power wires) to the junction block and see what happens
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I think you are on the right track and with Bhap's suggestion you should see some improvement. Franken is right about the voltages and as he says, your system is working but you are seeing some voltage drops in the headlights and
possibly some other loads as well.
There is a common belief that the alternator is just there to charge the battery and the battery is the main power source. Actually the opposite is true. The alternator is much more capable of suppling amperage to multiple loads than the battery and it will supply the same amount of voltage to all if the wiring is correct.
You're system uses the voltmeter to measure the voltage at the point in the wiring where it is connected. This may be less than the actual voltage in other parts of the circuits, which is what you are seeing.
To answer your Question. The L wire can be supplied by any 12 volt source including the battery positive post as long as you remember to wire a resistor in series with it to protect the diodes in the alternator. The word is that the resistor must be at least 35 ohms. Most professionals would say that you should use at least double that to be safe. The factory used a 10 ohm resistor in the 64 to 74 year trucks. They accomplished this with the charging light and the resistance wire off the key switch in case the light bulb burned out. It would back up the resistance and also provide a circuit to the alternator. The gauge dashes didn't have the light but they do have the wire.
I'd have to check the 74 and later models to see what they used. If I see it in the diagrams I'll post it.
Before I forget to mention it, if you run a L wire directly off the battery positive post you must install a cutoff switch in the wire as well as the resistor or else it will drain the battery overnight and might harm the alternator. I only do it that way for troubleshooting.
When I installed the engine in my truck, I actually wired the alternator from a battery positive source a as well as the starter and ignition so that I could work from the engine bay and not have to run back and forth to the cab. I di install a switch in the wire for battery protection as I stated above.
In your case I would go to a main key on, power source, and install the resistor in the wire or use your adapter and you could replace the L wire.