What is this and why did it stop working? (Electrical Problem)

matt92vr4

matt92vr4

Member
Hello, I'd like to thank you in advance for taking the time to read this thread.

Summary: My dad bought a Model A about a month ago. It didn't run and the electrical was a complete mess. The good news for today is that we got everything running and made her maiden voyage of this century! Left the garage and returned under her own power!

Prior to the voyage, we re-wired everything and it was all working perfect. Somewhere within our 1/4 mile trip around the block the lights and horn all stopped working. Using my multimeter I isolated the problem down to the "black box". It is a black box mounted on the firewall. I'm new to old cars but the best I can tell it is the antique version of a circuit breaker. Please see the pics below and let me know what you think.

It has two posts on it. One labeled "IGN" and the other "FLD". The "IGN" is receiving 12v from the coil. The "FLD" is supplying 12v to the switch on the steering column. Prior to our trip it was reading 12v in and 12v out. After the trip it now reads 12v in and about 3.8v out. The backside has two "ceramic spring" contraptions in a V shape.

For kicks and giggles I bypassed this box for a couple seconds and all of the lights and horn worked properly.

I'm hoping I can replace this with a modern circuit breaker that can handle the load? Please let me know. I really appreciate your help. Thanks, Matt
 

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It looks like a regulator for an early Chrysler Product alternator??? Possibly, someone may have used it as a makeshift relay??? I would consider removing it & just join the wires together. WARNING this is just my THOUGHTS!!
It's hard when I can't see/touch the system. Bill W.
 
Looks like it may have been used as a voltage reducer, maybe the coil part of the "black box" was providing the "voltage dropping resistor". The only thing that is not easy to convert to 12 volts is the horn, so if it was me I would remove the old box, install a voltage droping resistor in line with the horn (in the wire that runs to the horn) and run everything at 12 volts. If you still have 6 volt light bulbs replace them with 12 volt ones, make sure you have a 12 volt coil, and you will be good to go, no more old parts being "rigged" to do something they were never designed to do.
 
afuncar said:
if your car is 12 volts you probably should have a 9 volt resister for points iginition.
Click to expand...

??? Resistors have nothing to do with voltage, they limit current (amperage). A 'voltage dropping' resistor causes a resultant measured reduction in voltage across a specific load, the voltage at BOTH ends of the resistor remains constant.

An ignition ballast resistor is a special type of resistor, called a PTC, or positive temperature coefficient resistor. When it is cold, the resistance is less, permitting more current to flow through the coil, giving a hotter spark. In about 10-15 minutes, it gets very hot and the resistance goes up about 50%. That reduces excessive current pitting of the points.

In all cases a coil with an external PTC resistor is far superior to a so-called 12V coil with no external balast. Those coils do not produce a hotter spark when cold, and physically run at a higher final temperature, resulting in shorter life.
 
According to this Wiki article ( http://en.wikipedia.org/wiki/Voltage_drop )the Voltage drop is calculated differently depending on if the Voltage is AC or DC.
Consider a direct-current circuit with a nine-volt DC source; three resistors of 67 ohms, 100 ohms, and 470 ohms; and a light bulb—all connected in series. The DC source, the conductors (wires), the resistors, and the light bulb (the load) all have resistance; all use and dissipate supplied energy to some degree. Their physical characteristics determine how much energy. For example, the DC resistance of a conductor depends upon the conductor's length, cross-sectional area, type of material, and temperature.
If you measure the voltage between the DC source and the first resistor (67 ohms), you will notice the voltage potential at the first resistor is slightly less than nine volts. The current passes through the conductor (wire) from the DC source to the first resistor; as this occurs, some of the supplied energy is "lost" (unavailable to the load), due to the resistance of the conductor. Voltage drop exists in both the supply and return wires of a circuit. If you measure the voltage across each resistor, you will measure a significant number. That represents the energy used by the resistor. The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor.
You can use Ohm's Law to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance.
64e461f6c2b16b9e0198d78188f5b723.png
. Also, Kirchhoff's circuit laws state that in any circuit, the sum of the voltage drops across each component of the circuit is equal to the supply voltage.

In alternating-current circuits, opposition to current flow does occur because of resistance (just as in direct-current circuits). Alternating current circuits also present a second kind of opposition to current flow: reactance. This "total" opposition (resistance "plus" reactance) is called impedance. The impedance in an alternating-current circuit depends on the spacing and dimensions of the elements and conductors, the frequency of the alternating current, and the magnetic permeability of the elements, the conductors, and their surroundings.
The voltage drop in an AC circuit is the product of the current and the impedance (Z) of the circuit. Electrical impedance, like resistance, is expressed in ohms. Electrical impedance is the vector sum of electrical resistance, capacitive reactance, and inductive reactance. It is expressed by the formula
9f7b52f13e894d53a9987b42c09d799f.png
, analogous to Ohm's law for direct-current circuits.
Click to expand...
 
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Thank you for the replies. The Model A was converted to a 12v system before we bought it. It has an alternator and 12 volt coil. It also has 12v light bulbs. It starts and runs good, but the previous owner never finished any of the wiring to the lights or horns. I also doubt that the alternator was ever hooked up. I'm pretty sure it has only been driven about 10 miles in the last 30 years and it was done with no lights and on battery power only. The way the wiring was when we bought it, it would not be possible to use any accessory.

The NAPA link above is exactly the same part. This is definatley a voltage regulator. Thank you for the link. Now I have to research to determine if I need to keep it for the alternator and whether or not I can bypass this for the lights and horn. Thank you.
 
Don't get confused by some of the posts above. It makes no difference if you are using an alt or a generator, both output "DC". And yes you will get a different reading from one side of a resistor to another when current is flowing.
 
matt92vr4 said:
The NAPA link above is exactly the same part. This is definatley a voltage regulator. Thank you for the link. Now I have to research to determine if I need to keep it for the alternator and whether or not I can bypass this for the lights and horn. Thank you.
Click to expand...

Do you know what kind of Alt was used? How many wires are coming out of the unit?

Normally the regulator IGN terminal gets 12V via the ignition switch, and the "FLD"
terminal gets connected via a wire to one (either) of the field terminals
on an alternator. The other field terminal on the alternator gets
connected via a wire to ground.
 
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Just a tip, those simple & inexpensive Chrysler regulators can be used on many externally regulated alternators. I used many on older Volvos, with a Bosch alternator to PEP up the system. The Bosch regulator was only rated at 12.5 to 13 volts, too LOW! The Chrysler regulator was rated at 14 to 14.2 volts, much better at 1/4 the cost! Bill W.
 
Thank you very much guys. I don't know what type of alternator is on there but after further inspection, one of the three posts is labeled "FLD". The other "BAT" and the last is "GRD". I think I need to run the regulator "FLD" post to the alternator "FLD" post and then use a different source for the 12v lead to the light/horn switch. I feel like I need to put a fuse in the 12v source. This vehicle currently does not have any fuses. What do you guys do to resolve the fuse situation? Thank you so much for your help. -Matt
 
Hi Matt, In for a dime, in for a dollar... I recommend to you that you get a glass fuse block of 4 to 6 glass buss fuses. With your 12 volt system, you can split up your electricals to fuse alternator, ignition, front lighting, rear lighting and horn, and accessories. Get a couple of 12 volt relays to wire to the lighting switch to activate high and low beams, direct 12volt in and out to the headlights. Very simple, and you can get cloth-wrapped wire and fabric wiring loom tubing to make the whole thing look authentic. It'll take you a day and a half to do if you have all the parts. Happy motoring!
Chris
 
Matt, I went back and looked at the wiring pictures you posted a few weeks ago. YIKES! :eek: I'm still having tremors. Based on your pictures (re-posted below) I STRONGLY suggest you get a complete, new authentic-looking wiring harness from Brattons or Snyders.

Don't further jury-rig stuff. Since you do not have turn signals you can get a complete body/engine harness with a signal-stat 900 lever already correctly wired in. The wiring harness through the firewall to the starter lug is a separate item, get that too. You also need an unbroken terminal box with lid before you start running any wires through it. Get the fuse holder that connects to the starter switch and put a 25A fuse in it. That single fuse will protect everything except the heavy battery cables.

The Chrysler alternator you have requires an external field regulator. The original Chrysler electro-mechanical jobs were very unstable and unreliable. About '72 Chrysler went to a 'flat-pack' electronic external regulator which can be used (With even more wiring mods!) but you may want to consider a different alternator with an internal voltage regulator to simplify things.

This is Matt's dilemma:
110516


110517


110518
 
WTF?!!??
My gut reaction is to rip all that stuff out and rewire it back to standard.

One of the things I hated about my Town Sedan was when I found out the hard way that a previous owner had changed the wiring around (made for some real fun when I had to troubleshoot a short that developed)
 
I'd agree with the fellas regarding changing the wiring. The Alternator you have appears to be an old style Y-wound [good alternators]. The 'thing-a-ma-jig' on the firewall that went bad is a voltage regulator. Just jump the 2 terminals and see what the ammeter says with the engine running at a fast idle, it should then show a charge. All the regulator does is control field current. I see you already have a ballast resistor for the coil[ the little white 'gizmo']. When installing a fuse, most fellas just install one off the main supply at the starter switch. But, as said, you certainly could use some new wiring.
 
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