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Old 03-09-2009, 09:29 AM
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Positive or negative ground?

Howdy all,
A quick question for you all. I have a 52 F-1 with the 215 OHV 6 cyl. It's been converted to a 12 volt system and it's wired for a negative ground. I've been looking into buying a stock radio for it but I keep finding ones that are set up for a positive ground.
Is my truck wired incorrectly? Should I have a positive ground on her? Is there a way to convert a positive ground radio to a negative ground without destroying it? I'm really confused because all of my gauges and accessories work flawlessly as is with the negative ground.
Thanks,
AJ
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Old 03-09-2009, 09:43 AM
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Im not to sure on the 100% correct answer for your question but my understanding is that most all 12V conversions have been negative ground. (stock trucks were 6V, POSITIVE ground) If your gauges are original then they must have a voltage reducer on them to make them work with the 12V system. I am pretty sure you can do this with a stock 6V radio aswell, but if i am wrong im sure soeone will come by and correct me. Hope at least some of this helped. Goodluck
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Old 03-09-2009, 10:41 AM
Julies Cool F1 Julies Cool F1 is offline
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12 Volt electrical systems begun in Ford trucks in 1956 were negative ground. And I can't speak for it being wired 100% correctly, but if it is12 volt and negative ground, then that is correct.

In a nutshell, no, you can't use a 6 volt positive ground radio in a 12 volt negative ground truck. You could reduce the voltage to 6 volts with a vol-ta-drop or similar voltage reducer, but the ground thing is an big issue.

There have been a few with discussions about how previous owners have "jerry rigged" in a positive ground radio, and yes it physically can be done, but it's VERY dangerous.

The radio has to be completely insulated from any other metal contact, then hooked up with dedicated power and ground wires. It makes the case "hot" in a negatively grounded truck.


Problem is if ANYTHING that conducts electricity (including you) bridges the case of the radio (including metal *****) and anything grounded in the truck you will "short" it. It'll fry that radio - guaranteed, let alone what it will do to the points of contact.

Last person who talked about this had a keychain that touched the radio in this set up, and he ended up welding the keychain (what was left of it after it burned) to the dash.

Just FYI, they make 12 volt negative ground radios that look original and are made to fit in the OEM space.

I'll give you a link to C&G Ford Parts (because I am most familiar with their web site) if you want to take a look. Once you get their site open go to the 32-56 Car and P/U catalogue and in the "Search by Item Description" box type in "USA"

Here is the link:

C&G Early Ford Parts, (online)
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Old 03-09-2009, 10:44 AM
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You have a bigger issue than the ground...the stock radio is most likely 6 VDC, and not 12 VDC. I would ask the question, "why do you want a stock radio?". The truck is already been modified for 12 VDC so it's not still original, why bother with a stock radio. If it's merely for cosmetics, then look for one of the newer radios that have a "stock" faceplate but modern electronics...seems to be the best of both worlds. Good luck...
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Old 03-09-2009, 11:02 AM
Julies Cool F1 Julies Cool F1 is offline
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Hey Charlie! Think we were typing at the same time?

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Old 03-09-2009, 12:52 PM
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Quote:
Originally Posted by Julies Cool F1 View Post
The radio has to be completely insulated from any other metal contact, then hooked up with dedicated power and ground wires. It makes the case "hot" in a negatively grounded truck.
In addition to the power and ground wires. you would have to isolate your antenna from the car body. (I did this back in the '70's on a British Hillman I owned...back when I had more brain cells but less knowledge.)

I don't know for sure, but I think the lack of a good ground would open up the possibility of RF interference (alternator whine, etc).

Best not do it.
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Old 03-09-2009, 01:09 PM
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Quote:
Originally Posted by lonestaraggie View Post
Howdy all,
A quick question for you all. I have a 52 F-1 with the 215 OHV 6 cyl. It's been converted to a 12 volt system and it's wired for a negative ground. I've been looking into buying a stock radio for it but I keep finding ones that are set up for a positive ground.
Is my truck wired incorrectly? Should I have a positive ground on her? Is there a way to convert a positive ground radio to a negative ground without destroying it? I'm really confused because all of my gauges and accessories work flawlessly as is with the negative ground.
Thanks,
AJ
The answer is yes it can be converted. It's a simple matter of rewiring in the power supply and changing the vibrator to a 12 Volt unit. Some series resistance needs to be added to the power transformer's primary winding and the the tubes need to be changed to ones with 12 volt filements or wired in series pairs if there is an equal number of them. I usually eliminate the HV rectifier tube and replace it with a diode of higher current and voltage rating. That just makes one less tube filement to draw down your battery. You will not need to isolate the radio or antenna if you do this conversion. Occasionally I do these conversions but it usually amounts to fifty bucks in parts and one hundred bucks for labor. In the long run youn might just be better off getting one of the 12 V. repros which also has the FM stereo. Isolating everything usually ends up in disater with a fire. For one thing all the buttons and ***** are hot in respect to ground. Isolating the antenna shield also greatly effects the reception and sometimes eliminates it. Hope this helps.

Later man...
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Old 03-11-2009, 10:31 AM
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Hey all,
Thanks for information. I think I'll skip getting an original radio for now. It would just be too much trouble to bring everything back to positive ground for the sake of a radio that only receives talk radio around here.
I am interested in looking into the modern reproductions but wasn't able to find one on the website you mentioned Julie. Do they look identical to the stock radio? I've seen some advertised that fit the opening but had a very different display.
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Old 03-11-2009, 10:31 AM
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