VCCA Home Forums TECHNICAL - GENERAL Radios, Tools, Accessories Power for 1951 Truck Radio

Previous to this, I have only seen instructions that call for the 1951 truck radio to be wired through a fuse, directly to the feed on the ammeter. This is the correct wiring according to the GM instructions for the US version.

Now I find these instructions for the Canadian radio installation.

http://chevy.tocmp.com/1951gmradios/GMR27.htm

This radio is a different radio, used in some sedans, and actually has an additional tube because of the push/pull output. These instructions show a connection to the ignition switch, which of course is better because you can't leave the radio on accidentally.

I am trying to figure out why the two installations are different. I always thought that the ignition switch was not rated high enough to take the ignition, gas gauge, heater and a radio.

Hi old216,

I read those instructions differently than you. The live side of the ignition switch would be the constant hot side of the switch. The other side would be the switched side. I'm sure this is all based on the Canadian instructions.

The 1947-53 truck radio for the Chevrolet is different than the one described in the above instructions. The US Model has two leads in most cases. (If the on/off/volume switch ever failed it was replaced with a SPST (single pole, single throw) switch.

The two wires (yellow and black) are normally connected as follows: Black wire (A+) is connected to the switched side of the ignition switch or to the accessory terminal block switched side. It also can be connected to the non switched side or to the amp meter, however you must remember to turn off the radio when the engine is off as it will run the battery down.

The yellow wire is connected to the headlight switch at the dash light rheostat connection. When the radio is turned on and the headlights are off, the dial light does not illuminate. If the radio is on and the headlight are turned on then the dial light operates.

If the on/off/volume unit has been replaced with the SPST switch, the radio and dial light function in concert.

All the Canadian radios that I have worked on are slightly different than the US series of radios. In most cases they are interchangeable, however they may look different when mounted. The Canadian radios were assembled by a different manufacturer than the US.

AntiqueMechanic,
thank you for pointing out my mistake. Indeed the "live side of the switch" is in fact the same situation as the other instructions, ie: unswitched supply.

I find the fact that the replacement switches for the Chevy radio didn't include the dual switch interesting. I would think that they must have had a high rate of failure.

That Canadian radio is quite different, and it was used in some cars. The width between the controls can be adjusted and so can the angle of the face.

Thanks again for your reply.

Fred

Suppose for a minute that when the truck was new the owner would take good care of it. He wanted everything to work as designed. But a truck being a truck would beat a radio (or any other instrument or accessory) to death. So DPST switches would have been available in the early 50's to repair the radio as designed. As time went on, it was not profitable to continue the original type switch, but the SPST, which may have fit more than one application, could be produced for less money. By this time the truck and the radio are no longer new and the owner not as fussy. A switch that worked and still made the dial light function was accepted.

As a sideline, the on/off/volume control for the 1947-54 truck radios, are almost impossible to find and almost every radio received for repair needs this unit. Sever times the unit is destroyed by mishandling, specifically by shoving the shaft back through the unit and breaking the bakelite.

Ray,
is the practice of supplying the second contact via a miniature relay thought to be "correct" ? I know that changing some small details on these popular truck radios can really change the perceived value.

Fred

If a relay had been used from the start we would have many more operating radios. Too late now as you still need a functional switch to operate the relay (which came first, the chicken, or the egg)?

Operating these radios with a resistor on a 12- volt system is a NO-NO. If the owner is putting the radio in a 12-volt truck and advises me prior to the start of restoration I rebuild the radio as a 12-volt unit. Then no resistor is needed.

IMPORTANT INFORMATION: Almost every radio restored currently is fitted with solid state devices. They MUST be operated as directed by the repair shop as to the proper voltage and type of ground (+ or -).