After two months of working on my car it still has one of the main problems I took it apart for to begin with. Sorry if this comes out long but I want to give anyone here to help all the details.

The wiring harness was pretty much all original on my 71 Challenger. Stock style 2 field alternator and voltage regulator on the firewall. At idle the lights dimmed badly, the radio cut out, and occasionally it would stall. If it was raining and I had the lights, defroster, and wipers on it would die every time. I got quite used to throwing it in neutral and feathering the gas at lights to keep it going. The battery is a year old Interstate group 27.

I took it to advance and had them test the electrical system and battery. The battery tested fine after a charge. Testing the charging system, the machine said "No Voltage". Which seemed odd because my factory ammeter would swing to both charge and discharge with what seemed to be the appropriate load / charging conditions. Took the alternator off and had them bench test it, worked fine on that machine. Put it back on the car and changed out the voltage regulator, checking to make sure the back was grounded. Again "No Voltage."

I thought I had a short in some of my switches, which turned out to be that the switches weren't grounded. But in the process of figuring that out I pulled every inch of wire out of the car to look for burned wires etc. Saw that my main charging wire, black at the bulkhead, was nearly burned through. AH HA! Drilled out the bulkhead connectors and ran new ten gauge wire through both sides, converted the headlights to run off of relays and ran a second ten gauge wire off the alternator stud straight to those ( yes I should have looked more closely at the wiring diagram and replaced it with 8 gauge, but figured it would live since no headlight amperage would pass through it). Added a few accessories like a factory ashtray light and glovebox light which all work fine as do the headlights and relays.

Also while I was at it I converted it to a '85 Toyota Denso alternator. The two 10 gauge wires I hooked one to the headlight relay system and the other passes straight through the bulkhead crimped and soldered to the rest of the original wiring near the original splice. Ran a 12 gauge wire off of the sense terminal straight to the stud on the starter relay. Removed the original green and blue wires along with the external voltage regulator and connected a wire from the IGN terminal to the remainder of the factory ignition switched wiring. I currently don't have anything connected to the LAMP terminal.

The car starts and runs great, no more dying from low voltage at idle with accessories on. But I noticed the ammeter mostly hangs just slightly on the discharge side. When I first start it, ammeter will read charge, sometimes pegging the needle for a second when it first fires up. If I step on the brake or turn on a blinker I can see if move to the discharge side. But mostly going down the road it reads a slight discharge.

Yesterday, I drove her around a while and parked at my bosses house. Went to start it up and the starter didn't have enough juice to spin the motor. In fact it made kind of a grinding sound, so I went ahead and replaced it. After replacing it still no start, I had to jump start it with my jeep. Fortunately I have a cool boss who didn't mind it being there overnight.

NOW, last night I pulled the battery and had Advance charge it overnight. It tests good, car starts fine now. Had them test the charging system. "No Voltage". Pulled the denso alternator off and had them bench test it, and it is putting out fine on the bench machine.

So where does this leave me? I'm pulling my hair out here. I haven't tested the fusible link for continuity but it feels solid not stretchy or weak like a burned out one (felt one of those before). And if I had burned out a fusible link nothing would work without the car actually running right?
If the ammeter was shorted out it wouldn't swing at all right? I personally put everything back in the dash and those connections were tight.

I guess my next step is to check the fusible link for continuity tomorrow. Then to see if I can reach the ammeter connections again to disconnect and run a small bolt through them, tape it up and have the car tested again. After that, I am straight up of ideas. Can someone please give me ideas, educate me on bad ammeter behavior, or point me in the direction of the nearest cliff I can drive the car off of while there is still a fresh charge on the battery?

Mike I wish I could help but I'm not up on the denso system when used on a Mopar. I would put it at fast idle w a good sized load & check what the alt is putting out (charging voltage) and what the voltage is at the batt posts (what the batt is recieving) as that is (as you know) the bottom line. the denso is not charging in the car but tests good? What's not right w it's (supporting) wiring? Wish I knew that system. EDIT not the FL nor the ammeter.

I have not used the internal regulated alternator, but it sounds like the sense wire will be drawing power all the time because it is not switched?
It also sounds like there may be some issues with wiring/connections?

With the engine running at a fast idle, Use a good volt meter (like a DVM that should read to the hundreth of a volt) and measure the voltage at the alternator output stud to the alternator case, then from the alternator output stud to the battery negative terminal. If they are not the same, you have a bad ground connection. Next measure the battery voltage at the battery terminals, then the voltage at the ammeter and the point where the sense wire is connected. You will likely see some voltage differences in the measurements, and depending on what the differences are may show where there is unwanted resistance in the wiring.

Found it! Stumbled across the answer in a lotus forum of all places.

Every diagram I have seen, including the one supplied with the bracket kit from Mancini says the warning light terminal is "not used". That's BS apparently , at least for the '85 toyota design. The warning lamp has to be hooked up to a switched source as well, as it is the source of exciter current at low speeds. The internal regulator handles the rest including all of the exciter current at higher rpms. Aside from this hiccup it has been a great upgrade so far. Easy to put on with the mancini brackets, and fairly easy to wire up (now that I have worked out the kinks anyway). It also helps that I stumbled across an former toyo technician at Advance that confirmed the bit about the lamp being the source of low speed exciter current.

Now I have strong out at idle with high beams, foglights, blower on high, and stereo up. The only problem is that my car is an automatic, and since it idles in gear now, my left foot doesn't know what to do with itself since it doesn't have to hold the brake while I feather the gas. There are worse problems to have I suppose.