1929, 1930, 1931 Packard Fuse Block Questions

[Guest Jeff Keiser]

One of the headlights on my 1930 Packard was not as bright when illuminated than the other lamp. While correcting what I believe was a poor ground circuit within the headlight unit I must have caused a short because when I turned on the lights, although they illuminated, I smelled a hot wire odor and quickly determining that the fuse block unit was very warm. I disconnected the battery and corrected the short in the lamp. I also noticed that the fuse on the fuse block was blown, but the headlights still illuminated which brings me to the point of this question which is how do the 1929, 1930, and 1931 Packard fuse block units offer any protection to the lighting circuits to which it is connected?

These units consist of one 20 amp fuse conected in "parallel" with a wire coil which connects the two fuse terminals, therefore with the fuse removed, all lights illuminate just as though the fuse was in place. I don't understand why the fuse blew since the light continued to operate after the fuse blew before the short was corrected.

It seems as though these fuse units offer no permanent protection. If I had not been working on the car and noticed the odor, presumably the fuse would have blown but the lighting circuit would still have been energized and illuminated.

A series of photographs of this type of fuse unit can be seen on Tom Wilcox's excellent web site called "Packard Paddock". A 1930 wiring diagram that shows the parallel wire coil in the fuse block unit can be seen on the Packard Club website.

I restored this car 35+ years ago and thought I thoroughly understood this car but apparently do not. Are all you 1929-1931 Packard owners as surprised as I am that your lighting circuits will operate without a fuse? What protection does this unit really offer?

[Rusty_OToole]

This is guess work on my part but what if packard put a resistor in parallel with the fuse.

In normal operation the fuse would carry the current and the lights work normally. In case of a short the fuse would blow but the lights would continue to work although dim. The resistor would prevent the wiring from burning up.

This would be a safety feature so your lights would not go dead at the wrong moment. You would at least have some illumination to travel at reduced speed and other motorists would still see you coming.

The odor you smelled was the resistor heating up and burning off 81 years of dirt.

Edited July 31, 2011 by Rusty_OToole (see edit history)

[Guest Jeff Keiser]

Thanks for the reply. Your theory makes a lot of sense and probably explains what I experienced. A portion of the owners manual description of this device reads in part "A resistor in the protector ( referring to the fuse block unit) will permit sufficient current to pass for operation of the lights but will prevent an excessive discharge of current through the short circuit that blew the fuse" This reinforces your theory. Any excessive current apparently bleeds off and passes through the fuse at times of high current flow therefore offering protection.

Thanks again. I feel better knowing that circuit protection does exist.

[petri]

I have a similar fuse block on my '32 Packard 900 Light Eight which I have almost finished restoring. I studied this device, in fact I took it comletely apart to try and understand it. Rusty's operational description is the same conclusion I came to. It's meant to be a fall back "get home" operation. The car and lights continue to operate even if the fuses blow but the resistor limits the current in case of a short.

By the way, I found it difficult obtaining fuses of the same physical size to fit into that fuse block. They may be out there but I didn't work too hard at it. I used common glass fuses 3AG, etc and increased their diameter by cutting small annular rings from 1/4" copper tubing. The rings fit tightly over the metal caps on the ends of the glass fuses and then the fuses fit tightly into Packard's fuse block.

Howard Petri

[Owen_Dyneto]

Assuming it's the same fuse as used 33-36, it's a standard NAPA part, # 782-1017 for 20 amp, 782-1019 for 30 amp.

[petri]

That's great. I'm off to buy some of those fuses today. The 900 needs 20 amp as I remember but I will check. Thanks for that very useful information.

Howard

[Guest Jeff Keiser]

Howard,

thank you for your comments. I believe the fuses are still being manufactured. They are 13/32" diameter and 1 1/2" long and are known as AGU type. I read somewhere that the A stands for automobile ; the G stands for glass ; and I don't remember what the U stands for. Buss, ( Bussman Manufacuring Co.) still makes them and Littlefuse may also. If the NAPA numbers don't work out you can often find them on Ebay. Search under AGU 20. You will find many of them made with gold plated metal ends which I think are used in modern high power automobile sound systems. These may look a bit out of place on a packard so you might be happier with a Buss.

The new fuses do have a larger filiment than the older ones with a thin (lead ?) wire but I assume a 1930 20 amp fuse will react the same as a new 20 amp fuse.

Jeff

[petri]

Hi Jeff;

Thanks for the proper designation AGU 20. This makes it easy to find them elsewhere. I bought some of the fuses yesterday from NAPA and they fit perfectly. They are glass and the ones that came with the car, which was original and unrestored and sitting since 1956, were wrapped in paper and were probably cardboard with brass ends. I think they were made by Littlefuse. Of course those fuses may not have been original. I'm very happy to get this information and to now have the correct size fuses. There's a wealth of information on these forums.

Howard

[Owen_Dyneto]

I don't know if it was original or a later service part but a spare fuse p/n 166330 in a Packard parts envelope was in my 1934 glove box when purchased in 1963. It had a glass barrel and nickel-plated end caps, pretty much a dead match for the current NAPA item.

[tbirdman]

There is a resistor in parallel with the fuse. Look at the wiring diagram. I discovered it while installing a new wiring harness and was using a ohmmeter to make sure I had no shorts. I couldn't figure out where the leakage was coming from until I studied the wiring diagram.