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Discussion Starter · #1 ·
My son and I are just about ready to start putting our 1970 back together. We will be installing new American Autowire under dash harness. Along with that, we will be installing a "Retro Classic" stereo. I would like to avoid hacking up the new under-dash harness.

Is there somewhere I can purchase the "radio side" and "speaker side" of the factory harness plug so that I can put that on the end of the new radio and speakers and then just plug the radio into the new under-dash harness?

Thanks for any input...
 

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Chances are the new radio will require a constant 12V as well as an accessory 12V and what I would do is get those connections from spots in the fuse block.

Below is the fuse block on my 68 and I have labeled the terminals as to what they do and by using 1/4" female terminals, you can plug into the fuse block to power different things like your aftermarket radio.

You can see in the below photo I have a brown wire with a right angle 1/4" female terminal plugged into my LPS tap and this is to power up an added light I put in for my heater controls. If I ever want to remove it, I can and I did not have to cut into any of the original wiring on the car.



Here is a later picture after I added connections from an aftermarket radio I have under the seat of my car and again, I was able to plug into the fuse block and get what I needed as far as power.



These male terminals in the fuse block are what I call "taps" and these are protected by neighboring fuses already in place in the fuse block. The factory put these there for adding original optional equipment such as a rear defroster, cruise control, CB radio, electric trunk release, and so on to where it was a plug-n-play type of setup and a mechanic at a dealership did not have to cut and splice into the factory wiring harness.

As for as a speaker connection to the factory ones, do you have just the indash speaker or do you have the factory dash and rear speaker, or are you going with aftermarket speakers ?.

Jim
 

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Discussion Starter · #3 · (Edited)
Thanks for the helpful information and pictures.

While I was rummaging around the garage I found the old "radio side" of the factory connector. I re-pinned that to my new radio harness.


However, the fuse box labels the radio slot as 10 amp. I don't have the best eye for it but it appears the wire in the car harness is 16-18 gauge.

I am curious if that 10 amp limitation is due to the stock radio limitations which is what I suspect or if it is the gauge of the wire in the harness.


I used one of the online calculators and it says at 15 amps 16 gauge is good for 4' and 18 gauge is good for 2.5' with 12 volts and a 2% voltage drop.

The harness measures out to almost exactly 2.5'. My thinking is that I can just put in a 15 amp fuse if it is indeed at least 18 gauge.

Any experience with higher draw aftermarket radios and factory connections is appreciated.


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I have been installing car audio for years and even with some of the new radio's having a 15A fuse on the chassis of the radio, the wire supplying that power is way to small and I doubt if even if the radio is at it's loudest volume, with the CD portion being used, it will never draw up to that 15A of current. While I have never done any controlled tests with actual current draw I have a feeling even though the radio might have a 15A fuse, at most it might only be drawing 8-10A of current. At low volume, the radio might only be drawing a few amps.

Keep in mind too that with a 10A fuse, at 10.000001A of current draw it will not blow. Depending on the design of the fuse, a 10A fuse can pass 20A of current for a while before it blows. Your radio will sometimes be drawing hardly anything and then for a split second to reproduce a bass note might need to draw a few more amps and then go back down to minimal draw after the bass note is no longer being reproduced or outputted.

While the below if for a style and design of fuse, it's made to where even with the fuse having a rating of 300A, the one can pass 1000A for 1 second before blowing while the other design can pass 500A for 1 second before blowing. If you look closer how the line curves, even though these fuses are rated at 300A, they can probably pass 400A for hours on end and not blow.



If you go to some of the companies that make fuses, you can find charts like above and then by connecting the vertical and horizontal lines, see where they intersect and get an idea as to what they can or cannot do.

Jim
 

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Thanks for the helpful information and pictures.

While I was rummaging around the garage I found the old "radio side" of the factory connector. I re-pinned that to my new radio harness.


However, the fuse box labels the radio slot as 10 amp. I don't have the best eye for it but it appears the wire in the car harness is 16-18 gauge.

I am curious if that 10 amp limitation is due to the stock radio limitations which is what I suspect or if it is the gauge of the wire in the harness.


I used one of the online calculators and it says at 15 amps 16 gauge is good for 4' and 18 gauge is good for 2.5' with 12 volts and a 2% voltage drop.

The harness measures out to almost exactly 2.5'. My thinking is that I can just put in a 15 amp fuse if it is indeed at least 18 gauge.

Any experience with higher draw aftermarket radios and factory connections is appreciated.


Sent from my iPad using Tapatalk
That's a good way of making a conversion adaptor.

Keep in mind though that back then, these cars did not have digital radio's or radio's that needed a constant 12V of power so if your new radio does require a constant 12V, the three wire connector you pictured does not have that in any of those wires. The yellow is an accessory 12V, the gray is a dash light circuit, and the black is a chassis ground. While one could possibly make up a conversion adaptor or splitter for getting a constant 12V from something like the dome light circuit or lighter, it might be easier to just tag into the fuse block's 1/4" tap.

As far as voltage drops for radio's, normally they have an operating voltage window in that the radio is designed to work with anywhere from let's say 8V and up to 15V. An issue I have seen is if the voltage is on the lower end on the supply, sometimes the output of the radio to the speakers is slightly reduced and then at a higher input voltage, the radio's amplifier is capable of a higher output wattage but everything else works just the same with the radio. Years ago with some designs of car amplifier's if the amplifier got 12V, it put out let's say 200W but then if the voltage was increased to 14.4V, then the output would increase to let's say 250W. Normally this 50W difference was never audible but some tweakers will swear that they can hear it just like they can hear the difference between having the speakers wired with standard 18 gauge wire VS a high end, 99.999999% pure copper stranded wire and the wires on both tests are only 6' long.

Jim
 

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Discussion Starter · #6 ·
You guys have been very helpful...

Here is my "Plan B" - Just so I only have to add one more wire more to the mix under the dash, I will connect to the existing radio harness for the accessory and ground wire. I will run a new wire to the fuse-box and connect it to the tap labeled "Batt". I am not certain (all the wiring is lying in a box) but I believe that is the same tap that runs the glove box light. The glove box light has a "piggyback" on it for a second circuit.

As a side note, the reason I am maybe over complicating this is because this is my son's first car and I am sure at some point he will pull this stereo out and replace it with something way more obnoxious. So, I am shooting for somewhat of a modular approach to the wiring of accessories. This will allow for the "Acc" tap on the fuse box to remain open in case he needs it for some other accessory in the future.

Solid Plan?
 

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You guys have been very helpful...

Here is my "Plan B" - Just so I only have to add one more wire more to the mix under the dash, I will connect to the existing radio harness for the accessory and ground wire. I will run a new wire to the fuse-box and connect it to the tap labeled "Batt". I am not certain (all the wiring is lying in a box) but I believe that is the same tap that runs the glove box light. The glove box light has a "piggyback" on it for a second circuit.

As a side note, the reason I am maybe over complicating this is because this is my son's first car and I am sure at some point he will pull this stereo out and replace it with something way more obnoxious. So, I am shooting for somewhat of a modular approach to the wiring of accessories. This will allow for the "Acc" tap on the fuse box to remain open in case he needs it for some other accessory in the future.

Solid Plan?
This is a factory "Y" wire plug for a factory cruise control I have and this was designed to where when the cruise got added, the left plug went into the fuse block and then left another end on the right for plugging in yet another optional accessory. On the original GM plugs, they are keyed to where it makes it more idiot proof as the locating tab only allows it to plug into the correct open spot in the fuse block or existing end from some other option already plugged into the fuse block.



I have had to work on cars that there are no harness adaptors available for either tying in at the radio opening or at the speaker ends and some times I rob connectors from some other harness adaptor to make things work and not cut into factory wiring. This way if there is an issue and the dealership says it's from cutting into the harness without them actually seeing how the connections are made, I can unplug what I have done, plug the original equipment back in and then go from there. Sometimes too I have had to work on new cars that are still under warranty and if there is a recall or whatever on the vehicles harness by making or using adaptors there are less hurdles to overcome. I've seen a lot of harnesses butchered through the years and my boss bitches sometime when I want an adaptor and he says just cut an end off but I ***** back harder and we finally get the right parts.

Hopefully if the radio ever gets changed in the dash, the dash doesn't get cut. I've seen this through the years and while it may not seem like much, I was SOOOOO happy when I took out the aftermarket radio in the dash of my 68 the dash was uncut and unmodified. My dash is a 1 year style and all of the ones I have seen for sale are mostly junk. This might not make a difference if one wants to have it modified but some of us like the old original setups left alone or have it to where it can be returned to the original look.

Jim
 

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Radio

I put a Dream Line AM/FM radio in my 62 awhile back. Looks like a factory radio but with more toys on it. Got the radio and installed it like the directions stated. The radio did it's job right up until I would drive the car and then it start shutting off. Called the company that made it and they told me to connect the power wire straight to the fuse box, I had spliced it into the ignition on wire.
Did what they said and it still kept cutting off. Called them again, they thought somehow the radio was not getting the require power all the time and the radio was turning itself off account of the low power supply. Milliamps or something like that. They told me to connect it direct to the battery positive and negative. I asked them about hooking it straight to the battery if that would hurt the radio. They stated that theradio had a overload protection sensor in the radio. Hooked the wires to the battery, spliced a 10 AMP fuse on the wire and everything worked fine. Somewhere in the 62's wiring it was losing just enough power to shut the radio down.
 
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