Jim__H

I'm installing a Retrosound Hermosa dash unit into my '77 and wanted to get some input into my wiring assumptions and plan. The factory radio had a plug with three wires - yellow (switched power) gray (tied to the dash lights and controlled by the variable resistor on the headlight switch), and black (ground). The Retrosound radio requires two power inputs, continuous and switched power so I figure the yellow wire is good for the switched but the gray is not good for the continuous power. The wiring for the courtesy lights conveniently runs right by the center console, can I splice off the orange wire and feed it to the Retrosound? If not, what would be better?

Thanks,
Jim

BLUE1972

Run a wire under the console to the battery and put a 15 amp fuse in-line in the battery compartment. Just follow the other wires under the parking break console.

I did 3 this way... works great...

Rotonda

The courtesy light orange wire is hot at all times, so that would work. My only concern would be the amount of draw on this 20 gauge wire. What does the retrosound unit draw at rest, with unit shut off?
Another source would be tapping the 12 gauge orange or orange/black stripe wire going to the power window relay, near the shifter under the console. If you use this wire, be sure to add an in-line fuse to the retrosound.

leadfoot4

I'm not an expert, but have installed a few aftermarket radios, over the years. Usually, there's a blank port in the fuse box, that is both unused, as well as has continuous power. It's a LOT closer to the radio, to go to the fuse box for the power. Secondly, the "continuous power" for the radio usually controls nothing more than the memory circuit, which retains your station settings and clock settings. It's a pretty low current draw.

Richard454

The "modern" radios (last 15 years) use the +12 constant not just for memory but to POWER the radio. The red (ignition)wire is just a trigger wire and does nothing but turn on the radio.

This was done for two reasons-

1) To help keep noise out of the audio- as the battery - constant +12V is usually cleaner- and if noise is present in the system -a simple solution most of the time is run a wire directly to the battery. This helps eliminate the noise as the battery acts as a filter. Using the ignition as a power source- isolating it is a lot more involved. Also a winner for the manufacturer - as only one noise filter is required- where as previously two were needed. As in the C3, the wiper is on the same circuit as the radio (yellow wire) and noise could easily be introduced into the power line.

2) In most installations- the constant source is usually a more "robust" circuit- or a higher current- larger gauge wire used -as in the cigarette lighter/courtesy lights as on the C3.

So if you have noise- go to the cleanest power source- the battery- just make sure you fuse the wire AT the battery.

The gray wire is for the gauge lights- make sure to cap it off.

The ground? Unfortunately the Retrosound's sort of have a reputation for noise problems- you'll be far better served running a ground wire along with the power wire back to the battery. This is because the antenna will also see a ground at the mounting (back of the car on the frame) and if there is a difference in the ground resistance the radio will pick up noise.

Richard

bmotojoe

Depending how your 77 is optioned, you may have unused cells at your fuse panel. Both are hot all the time and would require the correct wire size and inline fuse rating to your stereo. 1/4" F/M crimp connector will work in there. A little more work, just a single wire pull. Don't be the next Bubba story......

Jim__H

Thanks Richard and you other guys. Sounds like running two 16g wires back to the battery is the best way to go and at my current state of interior reassembly will be easy to do. I even happen to have a perfect two hole grommet in my grommet stash!

The Retrosound's current consumption at operation is 15A max and < 3.5mA when the unit is off. There is an inline 15A fuse on the supplied harness along with a circuit that looks to be for noise suppression although neither the promo info or manual describes what it is. I assume that I don't need to install another fuse in series with this one, right?

Jim

Richard454

Hey Jim-

YES- you need a fuse right at the battery to protect the wire- just in case it gets pinched or shorted.

The glass fuse is just protecting the radio.

And yes- the coil of wire and capacitor is for noise suppression- however running to the battery is the best.

ESPECIALLY since these cars are fiberglass - as metal cars have the benefit of the metal hood-fenders-firewall acting as a "shield" for radio interference.

Richard

leadfoot4

THAT'S what I was referring to, in my earlier post.

Jim__H

Got it, grommet is in and wires run. Should get the dash unit installed tomorrow or Saturday, I'll post a photo in case anyone is interested in what it looks like in place. I can tell you right now it won't look much like the stock unit though.

Thanks guys

ddawson

I had noise in the radio when I 1st bought the corvette. Could not find the issue.

So I rewired it like this. All power and ground to the battery. The yellow wire for on/off went to a relay. The stock wire ran to the relay to fire the relay so the stereo would get the turn on signal. Zero ignition noise.

Jim__H

I don't listen to radio anymore. I do listen to a lot of music either on internet radio (Pandora) or my own music files, both through either Bluetooth or an AUX connection depending on what car I'm in. Does the same noise risk apply to that usage as well?

Richard454

The last 15-20 years radios basically have the relay built in- as the ignition wire just triggers an internal relay - so it should not affect the audio. Notice the 'ignition' (red) wire for your radio has no fuse or filter as it only requires a very small amount of current.

The power and ground to the battery is the ticket.

Richard

Bergerboy

Hi Jim,
I've got this same head unit in my '69 Coupe for just over a year.
Been fighting "the whine" for the whole time, on and off, and I use Pandora via Bluetooth almost exclusively.
I've tried choke filters, and an inline RCA filter on the pre-amp outputs from the stereo, and even lined my inner dash with aluminum foil.
I had some success by hard-wiring a direct ground from the alternator straight to the frame, but then the whine came back - I may try a better connection to the frame.
I plan to try the direct power and ground leads from the head unit to the battery this weekend, to see if that helps.
What I get, is a high-pitched whine coming out of the speakers, that varies in frequency with engine RPMs.
The volume doesn't vary with engine, with volume control, even stays when radio is on Mute, or disconnected from the BT.
The only way to stop it, is to turn off the head unit.
We still got some detective work to do!

Jim__H

Wiring direct to the battery does make sense to me now that I'm thinking about it. I guess you will find out much, let us know. Just wondering, those chrome plated sheet steel pieces that surround the distributor, do they help with shielding at all?

Richard454

Bergerboy is referring to alternator whine- as the alternator creates AC voltage and it's converted to DC- some AC is not filtered and ends up traveling along the wires with the DC.

A test I would do first-is check how clean the alternator is- take a Voltmeter- put it on "AC" voltage and see what it reads at the battery. The alternator "AC ripple" should read less than .5V. The battery should be able to clean a small amount up with no issue. HOWEVER- if you add an amp- the noise can get introduced into the audio at the preamp stage (where as it does NOT change with volume)- most of the due to imbalances in the audio (AKA signal) ground versus the chassis ground. Often happens using different manufactures amp and radio or cheap RCA cables too close to a "dirty"power wire.

The ignition shielding?- the metal stops the small radio station- AKA the high voltage sparks from sending radio interference through the air. The reason vettes have this- is the fiberglass doesn't shield. And with the big blocks -GM went to the trouble to even shield the ignition wires! It really only affects AM radio -that being said the cheap Chinese distributors and ignition boxes can be VERY noisy. only solution is to get better stuff.

Richard

BLUE1972

Sometimes if you take / put HD - Freezer aluminum foil and ground it behind the radio on the firewall you can stop the antenna from picking up interference form the plug wires right behind the firewall.

Just remember AL conducts so make sure there are no bare wires...

SwampeastMike

With all deference to Richard454, it sure looks like the MAIN power for the unit is coming from the yellow (ignitiion/switched power) wire with the red (constant power wire) used only for the memory. The yellow wire is the one that's fused and if they use the very standard color coding and you wire as Richard suggested the radio will keep playing after you turn off the ignition unless you manually turn the radio off. Check your instructions!

While you can easily and safely tap into any orange wire you find in the general area for a constant memory only power source, ignition power isn't as easy to get. Unfortunately the radio fuse in our cars is only 10A and both the yellow (switched +12V) and black (-12V) are very low (22) gauge. Your easiest way to get more ignition power is to run it direct from the battery (as you plan) to a SPST relay then use the original yellow wire to power the relay coil and provide power to the radio only with the ignition on and the relay coil energized. Don't forget the in-line fuse in the new wire from the battery!

Richard454

Hey Mike-

The YELLOW wire on the aftermarket radios is the CONSTANT power source wire- so YES it is THE power for the radio. The red wire is the ignition trigger wire- pulls no real power.
Honda was one of the first manufactures to set a standard wire color- this was done in the early 80's. Of course back then Japan was making 90% of the electronics (Sony- JVC-Poineer-Clarion-Alpine-Kenwood) - and the manufacturers sort of fell in line and have been using it ever since. I actually worked for Kenwood right out of college (1986-96) and got my start installing car stereos to put me though school. Not an expert now.....but I used to be!!!

So again- no need to add a relay for the switched ignition source.

Here's the instructions-

SwampeastMike

Richard454:

Please accept my deepest apology. I was working from memory when wiring car stereos in the old days.