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January 31, 2018

Is the factory radio system in your Freedom Machine functional? If it's not, could you diagnose the culprit(s)? For many of us, installing an entirely different system would be easier than troubleshooting the existing audio equipment. Many original dashboards, kick panels and package trays have been violated by drills, saws and aftermarket stereo equipment as a result. And at every show we vend, we hear from people who have no idea whether the radios in their Freedom Machines' even work, let alone how to identify where any failures may be lurking.

Before we get rolling, please respect the effort that went into these articles. You may share these articles, but I ask that you cite the author and where you got it from (https://redirad.com/blogs/news) and contact us before publishing it elsewhere.

We are going to learn in this article series how to inexpensively diagnose an unknown and/or nonfunctional automobile radio system. Several qualified suppliers and helpful online resources will also be identified throughout. These articles are written for the hands-on car owner and will be explored in the following order:

  1. Confirming there's power to the radio and that the wiring is safe,
  2. Inspecting the speaker(s) and the associated wiring,
  3. Performing a simple but effective vehicle antenna test, and
  4. Non-technical radio testing and antenna adjustment.

Note that while the cars pictured in this series are from the 1950s and 1960s, the methods apply to any model-year vehicle.

Part 1: Confirming vehicle power.

From my experience, the two main tools that measure battery voltage are a test-light and a multi-meter. The test-light is easier to use but it doesn't provide nearly as much information as a multi-meter. Multi-meters (either analog or digital) measure voltage and resistance and sometimes current and capacitance, depending on the specific model. Figure 1 below shows an analog Volt Ohm Meter (VOM), a test-light, and a Digital Multi-Meter (DMM). If you do not presently own either a VOM or a DMM, I recommend you buy one (or two). NAPA sells a decent DMM (part number OTC 3509) for $25. There are lots of multi-meter tutorial videos on youtube.com if the owner's guide leaves you confused.


Figure 1: The VOM, Test-Light and DMM you'll find in my toolbox.  They all have their places in electrical measurements.

Presuming that you have a meter (or a test-light) and you understand how to perform DC voltage measurements, you must confirm that the radio is getting power. Locate the RADIO fuse on your fuse panel. With the ignition key turned to either the ON or ACCessory position, probe both sides of the glass fuse. The measured voltage will be the same when the fuse is healthy. With a test-light, you can only have a GO/NO-GO indication. With a meter, you can confirm that you have battery voltage (the actual number of volts) at the fuse. If you have battery voltage on only one side of the fuse, it's blown and time for a new one. For those vehicles that use color-coded plastic fuses, you need to remove them to inspect and/or test them. Fortunately, determining fuse health is easy by visual inspection.


Corroded fuse block terminals and/or oxidized end caps on glass fuses can reduce the available potential from the battery. Even if the fuse measures good I suggest that you remove the fuse (AFTER you switch OFF the ignition key) with a proper fuse puller (such as Bussmann part number FP-A3, see Figures 2 and 3 below); do NOT use a screwdriver.

 Figure 2: Bussmann Fuse Removal Tool with Glass Fuse.

 Figure 3: Bussmann Fuse Removal Tool with ATO/ATM Fuse.


Clean and inspect the glass sleeve with a damp paper towel and clean the end caps using a small square of fine Scotch-Brite. This is also a good time to verify whether the fuse you pulled out is the correct one for the job – many times I have found a 20-amp (20A) fuse in a 7-amp (7A) socket (BAD idea!). The owner's manual and chassis shop manual contain the proper fuses to use in each circuit. Lastly, when installing a glass fuse, orient its metal ribbon so that the wider part is facing you. That will make it easier to visually inspect in low-light conditions in the future. Every time I buy a car I will take the time to remove each fuse, clean the glass, burnish the ends, confirm that its type and rating match OEM specifications, and reinstall them for maximum visibility.


Now locate the radio's power connector. Oftentimes the speaker connections are also part of this connector. If this connector isn't labeled, obtain a copy of the vehicle's wiring diagram in order to make accurate measurements. With the wiring known, unplug the radio's power connector and visually inspect as much of the radio-related wiring as possible. Poor wire splices and cracked or missing wire insulation may cause a fire; take the time NOW to make things right. Once you have addressed that, once again energize the radio circuit. Measure the DC voltage at the radio connector's power terminal. If it is more than five tenths of a volt (0.5 V) less than the voltage measured at the radio fuse, a poor connection may exist between the load side of the fuse and the connector terminal. Switch OFF the ignition key and get a second opinion from an expert.


If the radio connector's power voltage is within specifications, reconnect it to the radio. Verify that an antenna wire is plugged into the back of the radio case. The (often) black-jacketed, 1/4-inch diameter cable usually plugs into the passenger- or firewall-side of the radio case. Verify that the radio is switched off. Switch the ignition key to either ACCessory or ON and carefully listen for a “thump” coming from the speaker(s) when you switch the radio on.


Got “thump”? That's a good sign. Still awake after reading this? That's a better sign!  ...We will pick up at this point in the next article.

Stay Tuned,

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