Wiring Diagrams.....Grrrrrrrrrrr!

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Model T Ford Forum: Forum 2008: Wiring Diagrams.....Grrrrrrrrrrr!
Top of pagePrevious messageNext messageBottom of page Link to this message  By E. Douglas on Monday, April 07, 2008 - 10:30 pm:

What is up with all the different wiring diagrams?
Each one seems different when it comes to the Ammeter wiring.
I am working on a 26, later car which has a generator.
Some wiring diagrams show the Yellow Battery wire going directly to the Ammeter, and then the short jumper wire going from the other side of the Ammeter over to the "Batt" terminal on the back of the switch..

Other diagrams show the Yellow Battery wire going directly to the "Batt" terminal on the back of the switch. Then the short jumper going over to the Ammeter.
What gives???????


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 08, 2008 - 12:15 am:

UH - I don't think so. I think you are confusing the HEAVY YELLOW with a different wire namely the HEAVY YELLOW/BLACK wire. The heavy yellow wire goes from the battery side of the starter switch up to terminal #3 of the barrier terminal block on the firewall. Terminal #3 is the third one from the left as you face the block. From there ANOTHER HEAVY YELLOW wire goes to the Drivers side terminal of the ammeter. A heavy YELLOW/BLACK wire then goes from the passenger side terminal of the ammeter over to the BAT terminal on the ignition/light switch. Then another heavy YELLOW/BLACK wire goes from that BAT terminal to terminal #1 (leftmost) on the barrier terminal block. Finally a heavy YELLOW/BLACK wire goes from terminal #1 of the barrier block to the cutout output screw terminal. For your info many of the repro looms have the wrong gauge wire for ALL or part of the YELLOW/BLACK wire runs of which there are 3. ALL 5 wires I have just described are supposed to be 12 Gauge wires but on many repro looms only the SOLID YELLOW wires are 12 Gauge while the YELLOW/BLACK wires are 14 Gauge. Compare the outside diameter of these 2 wires in your loom if you suspect you might have the wrong wires in yours. The solid yellow wires seem to all be correct 12 Gauge. There is a noticeable difference between the O.D. of these 2 different gauge wires. This can cause your headlights to be a bit dimmer than normal and also your voltage regulator won't work as well if you have one. Replace the 14 gauge wires with 12 Gauge and your regulation to your battery will improve and your lights will be a bit brighter at night too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By E.Douglas on Tuesday, April 08, 2008 - 12:56 am:

John,
Thank you for your reply. Check out the link below to see my frustration.

Are you saying this info posted by Texas T parts is incorrect? It sure is different than what you have stated.

http://www.texastparts.com/mm5/manuals/26-27WiringDiagram.pdf

Like I said above, I've found different ways of wiring...who is right?


Top of pagePrevious messageNext messageBottom of page Link to this message  By john curry on Tuesday, April 08, 2008 - 03:37 am:

e d, these are on my 24 2dr, maybe they will help. john


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robb Wolff on Tuesday, April 08, 2008 - 11:15 am:

Another perspective




Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Tuesday, April 08, 2008 - 11:27 am:

John's directions are totally correct, and one might expect they would be flawless. The Texas T diagram is also excellent.

One point not mentioned is that the Yellow/black Tracer wire can be connected as shown in the Texas T diagram or connected to the BAT position on the ignition switch, as both points are common with that short Yellow/Black jumper wire.

The recommended 20 Amp Fuse could cause some grief, if it blows with the engine running fast and the generator providing current, especially if the engine is powered by a TrueFire ignition system, as the voltage will increase to a level the Truefire cannot accept. The lights will burn out, if they are turned on. The generator will burn out, if the engine does not stop right away.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Warren Mortensen on Tuesday, April 08, 2008 - 01:29 pm:

Just joshing here guys, but what do you do when all the wires are dirt color? ;-) I've worked on a number of cars where there are only two colors; Light Dirt and Dark Dirt.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Bishop on Tuesday, April 08, 2008 - 01:59 pm:

In addition to the great pictures above, and John's advice, this is the diagram I've always used with my '26 roadster. Hope this helps some (this came off the forum a couple of years ago).
Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 08, 2008 - 03:01 pm:

The only difference between my verbage and the Texas T parts diagram is the location of the connection of the YEL/BLACK wire which they show as connected directly to the ammeter with jumper to the BAT terminal of the ignition switch while the correct stock location was for that YEL/BLACK wire to go directly to the BAT terminal of the ignition switch with the jumper over to the ammeter. If wires have zero resistance then electrically the diagrams don't differ. In truth the STOCK wiring which I gave you has the YEL/BLACK wire going directly to the BAT terminal on the switch for a good reason and that is that you want the lighting circuit to run off the generator rather than the battery so you want the path of least resistance to be between the LIGHTS and GENERATOR. The T lights are the single biggest load on the system so that is likely why Ford wired it with the lighting getting higher priority in the wiring resistance tree of connections.

BTW - the CORRECT fuse for a 20 amp system is sized typically at 1.25 times the carry current so if the carry current is 20 amps - a correct fuse would be 25 amps. Some have argued that a fuse is a bad idea since if it blows - the generator may get toasted along with the lights but think about it - HOW COULD YOU POSSIBLY BE BETTER OFF if a fuse rated at 25 amps needed to blow because there was more than 25 amps through it!! NOPE - I vote strongly that you install a 25 amp fuse at the location shown. I now sell a really neat weatherproof fuse holder and fuses I have found. Some of you bought them at Chicasha. If you need one send me an email since I don't have the web page done yet. It is cheap insurance against a fire and when that fuse needs to blow - LET IT BLOW since at that point - the life of the car is at risk and generator or lighting issues are way way down the line in priority. Regardless of who you buy it from - install a single 25 or 30 amp fuse in your T at the Starter Switch end of the Heavy Yellow #12 wire that is the main source of power for your T.

I am sure I will be taken to task again for using the forum for commercial gain but I frankly don't care who you buy your fuse holder and fuses from but do get a good one and install ONE MAIN FUSE. Fuses in general are NOT helpful because they are one more connection that can go bad but ONE FUSE is a good idea and the T wiring is so simple that you really don't need any additional complications caused by an exotic fusing system or breakers.

Just my .02


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck on Tuesday, April 08, 2008 - 03:10 pm:

John,

For those that want a fuse, do not want your voltage regulator, but want to protect their stock generator in the event it loses its load, why don't you come up with an SCR crowbar that will ground the output of the generator in the event that it's output ever exceeds, say, 10 volts?

I would, but nobody would buy it from me - but from you, I'm sure they would!

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 08, 2008 - 07:02 pm:

Why not just put a 5 amp pico fuse in series with the field winding of the generator when rebuilding it. The Voltage regulator of course has such a crowbar circuit in it. I disagree that they would buy something from me and not you if you showed them the value of it and it was cheap enough. Unfortunately many T owners would NOT understand what the product does or why they need it. Even really simple things like diode cutouts are not very well understood at all. I got a box of 3 cutouts returned (YES CUTOUTS - NOT VR's) from a dealer. He said they were returned by customer as defective. 2 were perfectly OK and the third one was burned to a crisp with the diode exploded. Since the generator is 1 ohm of resistance - how could you explode a power diode with only only 6 or 7 amps of current flowing even if it shorted. Clearly it was destroyed some other way than in normal service. The problem as I see it is really that it is very hard to manufacture ANYTHING that is cost competitive these days. Even something as simple as an SCR on a printed wiring board housed in SOMETHING would cost half way toward a Voltage Regulator to actually manufacture unless the quantities were huge. If I were developing the Model T VR today, the tooling costs would probably make its selling price more than double what it is. Any labor at all in anything will drive its price up quickly. As for the generator saving thingee, I think that most folks who read this forum are well enough aware of how to prevent generator damage such that a circuit would really not likely sell very well since most folks know what causes the generator to become unloaded and they simply address the source of the problem in the first place which is good I should think. In truth if it were not CHEAP to have the crowbar circuit added inside each VR - it would be hard to sell it outside the VR for what it would cost to house it in something and manufacture it. Since the printed wiring board is already there for the VR and all the connections needed are also there - it was cheap to add that circuit. I think you know what I am getting at. I had a fellow engineer whom I respect a great deal once tell me recently that if he were to mount one resistor on a printed wiring board and sell it as a product for less than $50 in the U.S. he would go broke if it was his company's only product. Brochures, marketing, sales, advertising, benefits, product liability insurance, energy...all are a heavy load in the U.S. that a product must carry. Most stuff has to be "high ticket" or made in China if the company making it is to grow and prosper. Since Fun Projects is not going to grow and I am 64 years old it certainly ain't going to prosper with me in charge either but I sure have fun making T stuff.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck on Tuesday, April 08, 2008 - 07:13 pm:

John,

My apologies. I did not know that the VR contained a crowbar circuit. I was just thinking about the folks that had a perfectly good generator that needed no rebuilding.

"Unfortunately many T owners would NOT understand what the product does or why they need it."

Agreed, now that I think about it, but it's more fun to give them the benefit of the doubt.

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By E. Douglas on Tuesday, April 08, 2008 - 07:24 pm:

Guys,
Thank you so very much for your help. This forum is terrific.
John R., I will follow your "original" style wiring advice and go from there. Your advice is also underlined by the other very helpful contributions, and terrific photos.
At least you can see that I was not crazy or seeing things with different locations called out for the ammeter wiring.....although I must be a bit crazy to be having so much fun with an incredible piece of machinery that is over 80 years old.
I'll try to not let any smoke out of the wires.
Thanks again!


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 08, 2008 - 11:55 pm:

Seth:

I certainly agree that it seems a shame to disassemble a working generator to install a fuse in series with its field to protect it from something that really should not happen. The real culprit was the mechanical cutout. It stuck open for sure eventually and that spelled doom for the generator. An SCR or other crowbar device would certainly be an aid for a system equipped with a mechanical cutout since sooner or later that SCR would save the generator. Diode cutouts don't ever stick OPEN so that failure mode is removed but they DO short if over heated and that spells doom for the battery but not typically the generator. Unfortunately while YOU have the knowledge to know all of what I am talking about - lot's of T folks still run mechanical cutouts and don't understand the risk they are running and they are the very ones who could really benefit from your device but they could benefit from a diode cutout or VR too and they don't buy those either. Oh well - I still think some sort of crowbar is/was a good idea and I have never regretted putting it in my VR even though I really have no idea how many times it has been called upon to save anything since it is self resetting.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 08, 2008 - 11:59 pm:

Seth:

I certainly agree that it seems a shame to disassemble a working generator to install a fuse in series with its field to protect it from something that really should not happen. The real culprit was the mechanical cutout. It stuck open for sure eventually and that spelled doom for the generator. An SCR or other crowbar device would certainly be an aid for a system equipped with a mechanical cutout since sooner or later that SCR would save the generator. Diode cutouts don't ever stick OPEN so that failure mode is removed but they DO short if over heated and that spells doom for the battery but not typically the generator. Unfortunately while YOU have the knowledge to know all of what I am talking about - lot's of T folks still run mechanical cutouts and don't understand the risk they are running and they are the very ones who could really benefit from your device but they could benefit from a diode cutout or VR too and they don't buy those either. Oh well - I still think some sort of crowbar is/was a good idea and I have never regretted putting it in my VR even though I really have no idea how many times it has been called upon to save anything since it is self resetting.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Sven on Thursday, April 10, 2008 - 01:13 pm:

Dear John,
Does this third diode in ”2 were perfectly OK and the third one was burned to a crisp with the diode exploded” actually mean that your old saying that diodes never fail open has to be a little modified to “almost never”? Ha-ha (Think you can handle that)
Best regards, Sven


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, April 10, 2008 - 02:16 pm:

Actually it was still shorted but the housing around it was exploded so NO I don't have to modify my statement for THAT ONE but in truth I have indeed seen some diodes blown apart after shorting and they are then NOT shorted anymore ha ha. I sometimes wonder if these guys use a nail for a fuse. What I find sort of comical is that these guys will often send along a note that says "I was just driving down the street and it quit???" I then find parts missing from inside and weird hardware used that never was used here but they swear they never did anything but mount it and drive. Oh well.

For the record we don't use ANY phillips head screws so guys if you are gonna claim a warranty failure - at least don't send it back with internal phillips head hardware like some we have gotten back that "just quit during normal driving" haha.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Arnie on Thursday, April 10, 2008 - 02:32 pm:

Mr. Robb Wolf:

Can you please explain the optional ground that appears to be from the case of the ammeter to the switch plate/dash mounting screw????

What is its purpose or what does it do?

Thanks,

Arnie

P.S. I hope I'm not to old to learn!!!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robb Wolff on Friday, April 11, 2008 - 11:08 am:

Arnie,
Perhaps someone who knows more about electricity than me can explain the. The wire was soldered to the ammeter by a previous owner. I assumed that it wasn't getting a good ground to the dash so someone added the jumper.
Robb


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thomas J. Miller "Tom" on Friday, April 11, 2008 - 11:51 am:

Was there a light fitted to the ammeter or elsewhere on this switch panel? That would be the only reason to ground it. Otherwise, the switch and ammeter would work fine even if they were bolted ungrounded to a wood dash.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Friday, April 11, 2008 - 09:23 pm:

Sometimes people get an errant shock from HV leakage coming from bad coil box wood back through the coil box power wire. They get rid of it by adding a ground wire to the part that is shocking them rather than realizing they need to replace the coil box wood. Seen it on a couple of cars but it also could very well have to do with a light as Tom suggested might be the case.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, October 23, 2008 - 05:49 pm:

That bad wood in the coil box problem plagued me for about ten years. I did an engine rebuild and three valve jobs that did not help at all.

The engine would about run normal on Bat, but the higher Mag voltage drove it bananas.

An important clue that I over looked was an original, but badly burned New Day timer, caused by the spark voltage going back down the ground wire.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, October 23, 2008 - 05:52 pm:

Another consideration is the 1926-1927 Model T and Model A use the same ammeter. The Model A is positive ground and the Model T is negative ground. The Model T ammeter terminal wires may have to be reversed from the orginal drawing for a correct reading ammeter.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John H on Thursday, October 23, 2008 - 06:21 pm:

If the generator field winding can supposedly handle 5A before self destructing, then if the 3rd brush is set for 5A charge current it would appear that protection is automatic, as the generator is a constant current source.
Prior to rebuilding my cutout, there were periods where the generator was running unloaded (maybe for 20 mins at a time) and there was certainly no overheating of windings. The generator had been set to 5A before I got the car and I've never changed it.
There's enough room to stick a zener diode and SCR inside the mechanical cutout if one wants to be cautious.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Thursday, October 23, 2008 - 07:25 pm:

John H
I think you may be confusing the two different generator current circuits.
The third brush, based on it's adjustable position, obtains only a portion of the total armature current and feeds it to the field windings (1). This is the portion of the Model T generator circuit John Regan recommends be fused at 5 Amps. The philosophy is that if the generator charge output (2) rises too high because no battery is connected the field current in the third brush portion of the circuit will rise over the 5 Amps rating, open the circuit and completely shut the generator down. Thereby saving the generator from destruction.
I will give you the point that the position of the third brush will affect how long it takes an unloaded Model T generator to destroy itself, but only to the extent of how long it is driven that way and which part fails first, the armature or the field winding.
The Fun Projects VR has all the protection you need, but you must be mindful of how ammeter readings will differ from a stock Model T.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug on Wednesday, November 05, 2008 - 09:38 pm:

What is the proper gauge wire from the field windings of a Model T generator to the brush terminal screw? Does the insulation on this wire need to be high temperature rated, or just standard automobile wire? Is the same gauge wire used on the other brush connection?

Thanks!


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