Typically and idiot light circuit has the generator/alternator output going to one terminal and the battery going to the other terminal. If everythingis working correctly the light stay off because it has 12V (approx) on both terminals due to the opposing currents. When there is a problem like the genterator/alternator not charging the current can then flow and light the idiot lamp.
If you can determine which wire is the generator/alternator output circuit and attach that to your new gauge you should be ok.
I would recommend consulting a schematic to make sure of the circuitry. I'm sure that someone a bit more knowledgeable will pipe in momentarily and fix you up
Bobby nailed it. One wire comes from the gen/alt, the other from the I post on the ignition switch. The easiest way to determine the correct wire, if you can't visually trace it, is to simply turn the key to on, without the engine running, & check the voltage at both wires; the ignition switch wire should be the "hot" one, the gen/alt should be dead. That's assuming it's wired the same as original. Make sure you remove the other wire, or insulate it well somehow.
If you're thinking of the "self-exciting" feature, you can tap that pretty much anywhere; for example the 10SI GM alternators on OE systems tap it off the main power wire, usually about six inches from the alternator itself. Some actually tap it off the output post on the back of the alternator. It's really better to go somewhere downstream, like the fuse panel, so the alternator gets a truer voltage reading of the whole system. On the 10SI (the most common alternator, especially in the aftermarket hot-rod stuff), they have two terminals, plus the battery post. One is used to excite the alternator, the other is for the idiot light.
So, I guess it depends on what he's got, & how it's wired. I know the original Ford wiring harness shouldn't cause a problem, but if it was rewired to self-excite that way (& I don't know for sure, never having tried it, but I'd guess there's more to it than just the simple bulb; otherwise wouldn't the light always be on, since current would flow one way through it?) then it would have to be corrected.
Hopefully all that made sense.
Last edited by Homespun91; 07-05-2005 at 10:44 PM.
Well, my recollection is that it just uses the load of the bulb to create a small flow thru the field or stator, which is all it takes to kick it off. It doesn't need to stay lit because there are "real" loads once it's running. I just remember in the '70's era that dead batteries could result from a burned out idiot light bulb. Can't remember if it was FoMoCo or GM or MoPar systems that were set up that way, but I'm thinking I took note of it because my old man owned Fords back then.
The closest thing I could find to this, at a quick glance, is the older '60s Autolite (or Leece Neville) alternators with the external regulator & a charging light. The schematic indicates a 15 ohm resistor wired in parallel with the charge light. One side is wired to the ignition switch, the other (eventually) to the field current supply diode. I've yet to figure out the whole nuances of the regulator, it's kinda goofy (I was raised a GM boy & converted over in the '90s), but this would seem to go along with your memory. The bulb being dead shouldn't cause the alternator to stop charging, UNLESS the resistor was also burnt out (so the bulb formed the only circuit). The setup for an ammeter is slightly different & has no resistor, & the field diode is basically hot-wired (eventually) to the battery post on the starter relay. The ammeter is wired in a totally separate place & does not represent either a load, or voltage, to the supply diode. This method is similar to the 10SI version I described earlier.
At any rate, we can possibly assume this general approach was used by Ford into the '70s, until the external regulator was eliminated. Dunno about Mopars, but '60s/'70s GMs are different, at least what I've worked on.
So, the next step, I reckon, is to find out what charging system Todd has current-ly. (Yes, I know, that was bad. ) The original '53 setup wasn't wired like the later system I just described. With any luck he has one o' them newfangled internally-reg'ed alternators & can wahr it up diffrunt if needed.
Thanks for the great info Guys
My system is 12volt, with a 12 volt generator.
Homespun, if If I install the "original looking" battery gauge using your description as to how to do it, could I splice the generator wire from the new gauge Back to the idiot light?
I'm thinking now of mounting it under the dash instead of getting rid of it altogether.
Thanks for your thoughts,
As for the idiot light, the two wires for the original are connected across the regulator cutout relay contacts. One of the two wires goes to the armature (A) terminal on the generator regulator, and the other one goes to the ignition terminal on the ignition switch. When the key is on and the motor is not running, there is 12V (on your 12V system) at the ignition terminal on the ignition switch, but the generator regulator cutout relay is not engaged and there is zero volts there - thus the idiot light lights. When the engine is running and the generator is working properly, the regulator cutout relay closes and the voltage at the armature terminal (A) on the regulator goes to system voltage (12V) - thus the light goes out.
The replacement gage you bought really can't be a replacement for the original gage-type charge indicator since it has two terminals on it and the original just used a few turns of the actual charging circuit wire around a bar on the back. I suspect the replacement is really a voltage gage and just measures system voltage like more modern systems. In that case, connect the negative terminal on your new gage to ground and connect the positive terminal to the "B" terminal on your headlight switch - or anywhere you have access to a connection that supplies 12V only when the ignition is on.
Good luck with your project.
Oh, one other thing. Mike was talking about burnt-out idiot lights causing the alternator not to bootstrap itself and the battery going dead. Here's a neat little article that discusses the alternator in general and the burnt-out idiot light in particular. Enjoy. http://en.wikipedia.org/wiki/Alterna...ve_alternators
It's really all AL's fault, since he was the dirty dog who brought up the whole alternator/idiot light/not charging issue. I was merely trying to reassure him.
Also, note my clever disclaimer in my last post:
"So, the next step, I reckon, is to find out what charging system Todd has current-ly. (Yes, I know, that was bad. ) The original '53 setup wasn't wired like the later system I just described. With any luck he has one o' them newfangled internally-reg'ed alternators & can wahr it up diffrunt if needed."
The evidence clearly shows that AL is the one who should be taken out & hosswhipped.
On a relevant note, yes, I concur, to everything in your post. Now, you see why I live in fear & awe of you?
P.S. I wonder if it was the early original Ford systems (or somebody else's) that didn't have that parallel resistor, leading to the whole pesky minor non-charging thing?
Homespun91, Ford didn't do away with the external regulated alternator until the late 80's. Then they went to their internal regulated alternators. I have an '87 externally regulated alternator on my 302. Also you can wire these to have idiot lights or not. All you have to use the I terminal on the regulator.
That's interesting. I read your post this morning , & just out of curiosity got a chance to take a look at a couple of '80s Fords today: a '82 Crown Vic (302) , a '83 F-150 (351W), & a '82 Mustang (5.0 or 302, whichever you prefer). The Vic & truck had internal regs, the Mustang external; the Vic & the Mustang I know are original, the truck looks original but I dunno for certain. The only late '70s Ford I remember for sure was a '78 LTD 351W, also internal reg. My parents don't have it anymore, but Lord knows I fixed it enough to remember every detail.
So, I'm thinking it's possible that they might have used both systems for a while through the late '70s- mid '80s, depending on the car/drivetrain/intended use. Or, knowing Ford, it could have been decided by what the systems engineer had for lunch on design day. I don't know much about '80s-up Fords, so I don't know where the line falls, but that's what I found on lunch break, anyway. Don't think it helps Todd any, though.
It think they did use both at the same time. My engine is from an '84 mustang. Ford has had two different internally regulated alternators. The 2G which had some problems starting on fire and the 3G which is great if you want a lot of amps. You can find 130 amp ones in 90's Crown Vics but you may have to make some adjustments to get it to fit (it's big).
That sounds typical of Ford running both systems for years. I worked with GM throughout the 80's and early 90's. Cadillac had a beefy 120 or 130 amp alternator and on more than one occasion they came in on fire. They would get so hot that they would ingite the inuslator plate between the diode stack. I'll be running a GM alternator on my engine due to the fact that I'm running a 500ci Caddy engine.
I think Todd got the info he needed (I hope) maybe he will give us an update and let us know how it worked out for him (hint, hint)