Fried Ammeter

[MN_Ford_Fan]

Was finally able to get my model T to the point I could take it out on the road for the first time since I've owned it. Got about 3 miles down the road and everything was going good when it just died. I was running on battery at the time. The starter still worked, but coils would not buzz. After digging around, found that the ammeter had fried and cut the power to the key switch. The car has the reverse cutout on the generator. I also noticed a small puddle of water on top of the battery and the battery was warm. I hooked the yellow battery wire directly to the key switch, in place of the jumper from the ammeter and the car fired up. But I am not sure if my generator is putting out excessive amperage and that caused the ammeter to fail? Haven't driven or started it since. Any ideas how to proceed to troubleshoot this? Could the ammeter have just been old and ready to fail?

[J1MGOLDEN]

The common scenario is that the cardboard ammeter terminal insulators shrink and allow the terminal to drop down, short to the case and draw maximum current from the battery and generator, which usually starts a fire and destroys the generator.

[Norman Kling]

This can happen with any short such as the wire between the generator and the ammeter or the headlight wiring. It causes too much current to flow and since there is no fuse in the original wiring, the weakest link is the ammeter.
Norm

[MN_Ford_Fan]

Thanks. It is a new wiring harness so I'm confident that there are no shorts in the wiring itself. I do get intermittent headlight operation if I jiggle the connector. I did not have the lights on at the time of the melt down.

[MN_Ford_Fan]

I see in the forum history there is quite a bit of concern about the quality of the replacement 26-27 ammeters from the vendors. Are there other options available aside from finding an original used one? Can my burnt original be rebuilt?

[DanTreace]

The reproduction small ammeters are about all you can do. Rebuilding your original isn't possible. But you can use the original rim to replace the chrome rim on the repo to make it cosmetically nice.

Best to really check your wiring, and the terminals at the rear of the switch, as Ford recommended. Be sure none contact each other. Then be sure to use min. of 12ga. wire jumper for the switch to ammeter (some vendor replacement have been wrong size wire), that little jumper carries a big load.

Finally, add a fuse close to the battery on that major yellow electric supply wire at the foot switch, to prevent such a loss or fire. The fuse will blow if any place in the wiring or elec. components has a short to ground.

New repo ammeter w/o Ford script on lower left, with original bezel to disguise.

IMG_1607.jpg (121.4 KiB) Viewed 4346 times

[MN_Ford_Fan]

Thanks Dan. I wired in the fuse today. I put it up closer to the fuse block to keep it out of the elements but I like your fuse holder in the pics. May have to look for one of them. It appears that the generator survived the ordeal as I get 7 volts at the battery when running at a semi-fast idle. I believe the cutout works as well but have to test further.

[DanTreace]

The location of the fuse is good, easy access. The one by the footswitch is made by Fun Projects (Birdhaven), think the housing is a marine type single in line glass fuse waterproof container. Just keep in mind if something won't let you start the car to check that fuse!

The early 1919 starter Fords with the F. A. (Fred Ames) system had a fuse in line to the ammeter, that seems good, but for some reason, Ford deleted the fuse when making its own starter and generators. Likely at dumb idea, but I guess keeping the low cost Ford simple for owners. If that glass fuse broke or something, the owner wouldn't know it was the fuse and would complain to the dealer or maybe even cuss Henry for putting something there that made the Ford not start!

[J1MGOLDEN]

The only problem with the fuse plan is that if your engine is running on Magneto and the fuse blows for some other reason, the engine will continue to run and the generator will consume all the current generated and burn itself out.

[DanTreace]

Jim

True, but I'm running all my T's with Fun Projects Voltage Regulators, if a short there or other place the generator is saved by the regulator.

[MN_Ford_Fan]

Jim, Duly noted on the generator runaway issue. I read a few of the past arguments about that topic. The one that made the most sense to me stated that if you have enough amperage going through the wires to blow the fuse, frying your generator may be the better option among others, such as burning up your car. I do want one of those Fun Projects regulators but it looks like they are on back-order. I assume that's typical and one should just put in an order and wait your turn?

[Piewagon]

My general argument is always in favor of the installation of a 25A fuse BUT it must be located in the location that gives the maximum protection for the car wiring and not for the maximum convenience to replace the fuse. Your house if so protected would not have the fuse panel located in the basement where the power line comes into the house - it probably would be located in a closet on the main floor. That being said the correct location of the fuse is at the immediate source of the main car power and that is the battery and the logical place is at the foot starter switch as close as possible to the source end of the heavy yellow wire. You can easily get at the fuse at that location by simply raising the large bottom floorboard. Fires are started by the small gauge wiring of the T. The yellow main power feed wire runs along under the main source of fire wood (floor boards and wood dash if the car has wood dash). Put the fuse where it belongs as in the picture posted here and you have maximum protection of ALL the small wiring in the T. What too often happens is that when the owner has the fuse at the terminal block and adds a brake light switch he will pick up power for that switch at the closest source nearby which typically is NOT the barrier terminal strip but the battery foot switch. I have a habit of checking this out during car inspection and point it out to the owner. The first time you stand and watch a T burn up totally - you will realize that the fuse is not a convenience item.

Finally I also would point out that those who feel it is better to not have the fuse - trust me - your car COULD NOT BE BETTER OFF if there is more than 25 amps flowing in the heavy yellow wire at the battery end and there is no fuse to blow to stop it. The car is going to burn and the least of your worries is the generator. In truth if there is a SHORT that causes the high current to blow the 25 amp fuse then that short is to GROUND and the generator output is then also going to be grounded and will not burn out by that since adjustable third brush generators come from the factory with their output WIRED DIRECTLY TO GROUND with a red warning tag to not remove that ground connection until a battery and wiring is properly installed. OK I have said my piece. One thing I have known since day one and that is whatever scenario you can dream up and protect against generally doesn't happen unless you protect from ALL of them as best you can.

[J1MGOLDEN]

I have that Yellow Fuse Holder (that I got from John) in the proper place and that has not been any problem at all! I also had that Electronic Cutout that I got from John, but it went bad and they are very hard to get now. They are not too hard to convert to a just plain diode. That is still working OK! Then I might not need it anyway, if the T stays in the garage and is never used again.

[MN_Ford_Fan]

I was installing my new vendor supplied ammeter today and I noticed that with the wiring installed in the typical fashion you see on the wiring diagrams, the yellow from battery on the left post (as seen from face of ammeter) and the jumper to the switch on the right post, my ammeter read backwards. It swung to the charge side when lights were on. I switched the wires so the jumper is now on the left, again as seen from drivers seat as if looking through the ammeter, and now it reads correct (discharge when lights are on). Is this typical, or do I have something wrong?

[DanTreace]

Ryan

That is typical of those small repro 26-'27 ammeters. The vendors source from mfg. who just makes the one version for Model A's that use positive ground.
They do change the 30-0-30 to 20-0-20 face plate but the circuit inside the unit is still set for positive ground.

The meter doesn't care what direction the current flows, but the face plate does! Simple fix, just swap around the two wires on the back of the repro ammeter and it will read correct for your T.