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Posts Tagged ‘electrical’

Ignition Switch Changes

Thursday, February 11th, 2010

As with many other items on the Advance Design Series trucks, there were also changes in the ignition switches. Both Chevrolet and GMC shared their several switch changes during the seven year series.

In the beginning (1947-1948) a unique three position ignition cylinder and housing was introduced. This was a first for GM trucks. It related to a country with limited crime and a time when many people did not lock their houses. The switch allowed the truck to be started without a key.

By turning the cylinder and key to the far left, the ignition switch was locked. However, the middle position was the big difference! Here the ignition was still off but a small tab or teardrop extending down from the cylinder face allowed the driver an option. With a touch of a finger you could turn the cylinder clockwise with or without a key due to the teardrop.  This 1947-48 feature was convenient for many owners, particularly on a farm. No longer did they worry about losing the key or having to dig when it was in a pocket.

When the key was moved to the far counterclockwise position, the ignition was locked.  This security feature was built in.  The switch could not be locked without the key, so no worry about it accidently moved to the locked position.

This three position switch, also used on the 1948 Chevrolet car, was discontinued about the end of 1950. GM then returned to the two position on-off cylinder and housing that would not operate without a key.

Between 1947-1953 the switch and cylinder combination plus a one candle power bulb and socket was attached to a sheet metal housing. This assembly is screwed to the top of the lower dash lip out of sight. Only the round key cylinder face is seen by the driver. It extends through a larger hole in the dash. A resulting 1-1/16 inch circle opening between the dash and this cylinder face produces a lighted ring at night from the adjacent small bulb. This allows the driver to easily locate the switch in the dark.

In 1954, with the total redesigned dash, there was a complete change in the ignition switch housing. The threaded end of the die cast housing is held in the dash by a chrome lock ring. Only this ring and the key cylinder face is visible to the passengers. It is also the two position on-off type as the key cylinder did not change.

With the introduction of Hydramatic transmission during these years the switches did not change. The starter motor was activated by a button near the headlight switch not by the ignition switch.

1947-48 1949-53 (Both in lock position)

ignition switch 2

1954 Ignition Switch

ignition switch 3

1954 Ignition Switch with Light Bulb Socket Hole

1947 – 1953 Horn Buttons

Thursday, February 11th, 2010

Both Chevrolet and GMC used the same steering wheel during the 1947-1953 Advance Design years. To keep the two makes just a little different the horn buttons had a separate design. Thus, the driver was always given a close view of the name of the truck he was driving.

horn button 1

Chevrolet: Horn cap is chrome and then painted with steering wheel color. The raised Chevrolet letters and surrounding ridges are free of the paint so the chrome is visible (above)

horn button 2

Horn cap painted to match the steering wheel with red lettering. No chrome. (above)

Battery Shields

Thursday, February 11th, 2010

On the Advanced Design Pickups, the battery was under the passenger side of the cab floor. To protect
the battery from road debris (gravel, sand and ice) it was important that it be protected from this coming

from the right front tire.

Designers of the Chevrolet and GMC installed a metal plate riveted in place. A simple extra to what

might have been a problem to customers.

(On the 1946 and older trucks the batteries were only protected by their partial tray.)


1950 GMC 1 Ton


1953 Horn

Thursday, February 11th, 2010

In 1953 Chevrolet/GMC trucks adopted the more modern relay activated horn. To keep cost low, GM used the same seashell type horn that had been on Chevrolet cars since 1949. It displays the number “689” in its die cast metal. In the Chevrolet Master Parts Catalog, the number when ordering a replacement was 199687.

Though the 1953 truck used the existing car horn, GM created a special right angle bracket to attach it to the small extension on the iron intake manifold. This bracket has become very rare today. Most people incorrectly think the 1952 and older horn should attach to a 1953.

1953 horn 1













1953 horn 2

1953 horn 3

1953 horn 5









1953 horn 6












1952 and older horn position (above)












Just right on a 1953!

1948-1953 Horn Bracket Location Changes

Thursday, February 11th, 2010

The horn location on the intake manifold of the Chevrolet 216 six cylinder changed position with the addition of the accessory oil filter. This oil filter was attached to the front of the intake manifold. A special shaped horn bracket was necessary to move the horn forward away from the filter. This bracket was included in the box with the new oil filter package.

From 1947 and older, even the 3 speed transmissions shifted on the floor. There was no column shift. Without a shift box on the steering column, the oil filter could be placed on the rear of the intake manifold. Thus, the moving of the horn forward does not apply during these early years.

The attached photos show the two styles of horn brackets used between 1948 and 1953. On 1954 and newer the horn is attached to the radiator support.

1948 horn bracket 1

1948 horn bracket 2

1948 horn bracket 3

1948 horn bracket 4

Early Ignition Wire Protection

Thursday, February 11th, 2010

During the 1930s and 1940s many auto and truck manufacturers protected the long ignition wire between the dash switch to the coil beside the engine. The technology of wire insulation wrap during these early years was a woven cotton covering and it was more susceptible to damage from oil and antifreeze in the engine compartment. For protection, a metal wrap was placed around this electrical wire. See attached photos from a 1941-46 GM truck. A metal cap even covers the connection on the top of the coil for protection. It unsnaps to disconnect the ignition wire from the coil.

The cable system was very good 60 years ago, however, today it can create much frustration. The cotton insulation on the inside wire has deteriorated and pieces can drop away. In time the hidden wire gets exposed and may touch the outer metal cable causing a dead short. The engine stops with no notice. It may occur only on a rough road or during a fast turn. The engine may run well at idle or not run at all. One can imagine how difficult locating the problem can be. Opening the two ends of the cable and replacing the original wire may be good insurance. A modern vinyl covered wire will never be seen inside the original metal wrap.

Early Ignition Wire Protection 1

Early Ignition Wire Protection

1941-1946 Horn Parts

Thursday, February 11th, 2010

One of the more asked questions on the 1941-46 GM trucks is regarding horn contact parts. Most have been damaged over the years and new owners are unsure how they were originally assembled.

Below, is a diagram from a 1940’s GM Master Parts Catalog and gives an excellent view of the parts used in the assembly.

Most items are currently reproduced, including the upper bearing, rubber bumper, cap assembly, steering wheel, mast jacket, 3 finger horn cap retainer, and internal cap spring.

Note: Added are the available part numbers from the Jim Carter Parts Catalog.

Horn Contact Parts

Speed Up 6 Volt Starting

Thursday, February 11th, 2010

One of the more common reasons for slow engine turnover using an original six volt system is under size battery cables. Most of today’s auto parts stores only stock the smaller diameter 12 volt design. Unknowing owners mistakenly replace their original worn cables with shinny new ones that are as much as half the diameter as needed. Two ground cables are also required: One from the battery to the frame and one from a starter mounting bolt to the frame.

Six volt starters require twice the electrical flow to operate properly. Don’t blame your six volt system for slow unacceptable starter motor speed! Many restorers go to the expense of changing their 6 volt system to 12 volts. They feel their original system was inferior and believe what they did was necessary. The problem could have been corrected with just adding the three proper cables.

Remember: Millions of cars and trucks were made with 6 volt electrical systems each year. If they had not operated correctly they would have been built with 12 volt systems!

Battery Cables 6 Volt

Buy Parts for 1934 to 1946 Trucks

1967, 1968-1972 Hazard Flasher

Thursday, February 11th, 2010

The 1968-1972 hazard flasher unit is not self canceling as in 1967. The only way to cancel the later hazard flasher is to pull the knob out. This feature was incorporated into the 1968 truck so that the hazard flashers could be operated when the vehicle is being used for slow speed operations. It became a problem in 1967, when the flashers would self cancel when turning on a job site or related small work area.