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Another thing about getting it locally, if the part is bad, they can get you a replacement quickly without having to ship some it. My NAPA can get most replacements in 2 hours. When Advance tested my ALT and said it was bad, they told me, NAPA 4 miles away had the one I needed. That NAPA removed my 2 belt pulley and put it on the replacement.
That NAPA used to be a Carquest auto parts, that was bought by the owners of my local NAPA, 2.5 miles from my house. Seems these guy have their own support network. Carquest was a big local chain here back in the past.
I spend my whole sunday replacing the regulator, wiring and alternator with Rock Auto parts. In sub-zero weather.
Only to find that the dang thing, sporting a TEST:PASSED sticker, was showing a measly 12.3 V on the meter.
Took it to Oreillys 15 miles out, and the thing in fact turns defective.
Ugh! Im done with Rock Auto.
OK, so heres how the story ends, in case you're interested.
I took the truck to this guy's junkyard.. The guy's owned a few similar F100's and F150's and has a small shop. He looked into it for a couple days and said "the ignition wire was not doing its job " EG- tickling the alternator awake. We could see 12.8 V when I turned the key in the ignition sw, but once the engine was running, the wire went dead.
He tried but could not find what the heck was going on. In the end, he swapped the wire going from the Ignition to the Regulator'I' tab, with a wire from the positive coil post. And it works. I was able to test that the wirehas 0V while the key is out, but once the engine is on, we have 13.1 V. Now we keep getting 13.1 V after turning on the high beams, A/C, wipers and header lights while the engine is running. I definitely didnt need a 100A.
He asked for $75. I rounded it up to a well deserved $100.
Last edited by Rafael Suarez; Feb 10, 2025 at 08:38 PM.
Reason: typo
Good to hear you got it charging again but I dont think I would use the coil + as a trigger.
You are pulling power / load with that wire connected to the coil that it needs.
Try it and if you have running issues I would look at this first.
Dave -----
Do you really have 13.1 volts on the coil positive while the engine is running?
Do you have a stock DS2 ignition system, or something else?
Jim
I honestly have no idea about the DS2. But yes, absolutely. 13.1 V. My main concern at the time was that it would vampire drain the battery while the truck was off.
I am going to wait until Franklin2 comments on your modified charging system.
It seems like a bad idea in my mind.
General Info:
The DS2 ING system uses a ballast resistor wire to drop the coil positive voltage in half. If you turn the Key ON, engine not running, you should get about half of the battery voltage at the coil positive. Engine at idle, coil positive voltage is usually around 6-8 volts.
I believe you have a idiot light instead of an AMP Meter, if so the voltage regulator is wired differently.
Jim
The voltage regulator will work both ways, using the I terminal or using the S terminal for excitation of the alternator. The factory used both. The only problems I have had with tying the excitation wire to the same feed as the ignition coil, when you turn the engine off, the engine will not cut off right away but slowly die. The alternator system tends to generate a voltage back up the excitation line and this will sustain the ignition system for a second or two. But if he is not having this problem, or doesn't consider it a problem if he does, it should work ok.
Max Cap was on the money
I definitely didnt need a 100A. 
