Which Circuit Should I Tap for a Radio?

D

Dan Sarandrea (Phila)

Waitin' On Parts...
Installing a replacement radio in my '86.

The unit calls for two power connections, one to constant battery power and one to ignition switched power. I have provisioned the constant battery connection.

Which circuit (and what are the wire colors please) should I use for ignition switched power?

And has anyone noticed that the two links in the wiki for late model wiring diagrams are broken?
 
Clock

The clock wire harness is a convenient spot to get ignition switched power. The late model wiring diagrams show this as the orange wire on the car side of the connector. The the colors of the wires coming out of the clock do not match the colors of the wires coming from the car.

Should you want it, the yellow with black stripe in the clock harness carries the "lights on" signal.
 
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Suggestion for you Dan

As indicated, tap the "constant" +12V from the same feed that goes to the RED wire to the clock.
This line is used primarily to keep the memory of your stereo active. (low current)

But, I suggest you put a relay on the "switched" power (the power line that turns on the display of the clock) and feed the relay from a fused line from the battery post (feed) you made up.

That way, you can install whatever power-sucking stereo you want without affecting the lamps and gauges in your X.
The wire that feeds the clock isn't all that robust, but certainly good enough to power a relay.
 
bbrown said:
As indicated, tap the "constant" +12V from the same feed that goes to the RED wire to the clock.
This line is used primarily to keep the memory of your stereo active. (low current)
Click to expand...
Not necessarily, most newer stereos draw their power from the "constant on" wire and use the ignition switched wire only as a signal to turn the stereo off / on with the ignition.
 
True...

Not necessarily, most newer stereos draw their power from the "constant on" wire and use the ignition switched wire only as a signal to turn the stereo off / on with the ignition.
Click to expand...

This is how mine is. When I used the clock for constant power (in my X) I would have brown-out trouble when the volume was high. Look at the wire gauges, whichever is thicker of the red and yellow wires will need a dedicated circuit.

I would suggest a new fused circuit for stereo power, and if you can, a dedicated ground. This will help eliminate "ground loop" noise.
 
Yes, most get all of there power from the constant power source side. The switched side on most new units are just driving a transistor (mosfet or similar or running it through to the processor as an input) to switch the unit 'on', so in most cases in the new units the 'switched' side is very low current.

John
 
I ran a dedicated hot off the battery for both power sources on mine. Otherwise your key must be on to have the radio on and sometimes I like to have the stereo on when parked, don't really want the ignition on and all that "hot" just to listen to the radio. Of course the danger is you leave it on unintentionally and drain the battery. The lights on the stereo should be a warning but I have left it on once or twice, no big deal as it doesn't draw much when the volume is down.:music:
 
Dan Sarandrea (Phila) said:
Installing a replacement radio in my '86.
Which circuit (and what are the wire colors please) should I use for ignition switched power?
Click to expand...

I just installed heated seats in a couple 500s and used these for power;

http://www.zorotools.com/g/00094184/k-G2228694?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&kw={keyword}&gclid=CI6l-PvonLUCFUOK4AodUgIAEQ

Autozone sells them as well. This way you just plug in the fuse box with any extra strain on an existing circuit.
 
Thanks guys for your valuable info!

Yep, "upon further review" of the installation instructions (all pictures, no words) and the Bertone wiring diagrams, it looks like my Blaupunkt Hamburg MP57 head unit is like the more modern units you guys mentioned. The constant power connection needs to be a minimum wire dimension of 1.5mm and able to support a 10 amp fuse draw. The ignition switched connection diagrams note that this circuit draws a mere 300ma of power.

So it makes sense what you guys are saying, the constant power connection drives the unit and the switched connection is just an off-on signal.

In that case Bjorn's suggestion is the most convenient, just tap the orange wire to the clock for ignition ("hot in start and run" as the Bertone wiring diagram calls it) for the ignition connection.

I already used my nuclear power plant buss bar for the constant power connection:laugh: As Greg mentioned, will look again to see what I did with ground...I hear Greg saying that a dedicated ground will eliminate the possibility of ground loops with other items on the electrical system, so I'll do that.
 
Careful. I picked up from the clock wires as suggested earlier and I got some weird faults. The most amusing was the radio turning itself off but only when over 3000RPM with the right hand turn indicator on. :hmm: In our RHD country that usually meant that big-rev overtaking manouvers switched the radio off - which my friends unkindly suggested was so that I could better hear the valves bouncing... :laugh:

My head unit is a late model Alpine with integrated bluetooth and iPod charger/controller. Perhaps its a heavy current draw-er? I have a largish Alpine amplifier connected directly to the battery terminals which is switched by the radio, and a power antenna (using the car's wiring solely) but I can't imagine those things made a difference - but maybe? The car has an 85A alternator and an adjustable reg set at 14.1v.

Anyway - I rewired the earth direct to its own ground, the constant power directly to my additional fuse block and the switched line to the relay I added to my ignition circuit and everything is now rosy! Also cured the slight alternator whine I had when taking a call through the stereo.

HTH.
 
I would run the switched power source to the radio from a constant 12 volt source through a relay triggered by the key switch. That way the radio will stay on until the key is removed from the ignition.
 
Agreed!

Matthew said:
I would run the switched power source to the radio from a constant 12 volt source through a relay triggered by the key switch. That way the radio will stay on until the key is removed from the ignition.
Click to expand...

What I did was to use the power wire which led to the key-left-in-the-ignition buzzer.
 
Matthew said:
I would run the switched power source to the radio from a constant 12 volt source through a relay triggered by the key switch. That way the radio will stay on until the key is removed from the ignition.
Click to expand...

Brilliant! This was just put on my spring to-do list.

Thanks
 
I had to laugh when Franken said he eliminated the slight alternator whine when he took phone calls through his stereo. I usually have to pull over to take a call. I can't hear ANYTHING over the roar of the engine, the road noise, and the wind!
 
That's Because He Said...

"I have a largish Alpine amplifier connected directly to the battery terminals which is switched by the radio."

A "modest" Apline is probably good for 150W per. Largish could go as high as 300 :eyepop:.

I guess it is just comes down to what is more enjoyable, the sweet sounds of Italian machinery and mother nature or a phone call.

Please Franken, take all this in the lighthearted jest it is intended :nod:.
 
Dave80GTSi said:
What I did was to use the power wire which led to the key-left-in-the-ignition buzzer.
Click to expand...

what wire did you tap (color and location)? Did you use a relay? If so, how did you wire this up?

I want to do exactly this and use a relay so that there is no interference with any other circuits...

TIA
 
I run it off dedicated power line right from the battery, through the firewall, some will even put a little fuse block in there for all the accessories you might add, I just did an inline fuse though. This way the radio is independent of the key since there is no accessory position, you can't have your radio on with the car parked unless you power the radio hot all the time. You could tap an unswitched hot like at the ignition but I don't like loading any OEM circuit, they're taxed enough already, IMHO.
 
Just a thought....

Has anyone considered adding a separate relay for main power and then an accessory relay to keep the radio on until you open your door (with ignition off)?

Something like this might work, eh?
http://www.the12volt.com/relays/page5.asp#drto

...or perhaps a 3rd party accessory delay timer/relay config like many new cars have today.
 
I considered something along those lines to add "modern" convenience features to the radio, but then lo and behold I discovered by reading the accompanying user manual:innocent: that the radio I purchased (certainly nothing special or remotely "audiophile" by any means) already had a "forget" or "battery saver" feature, in that it will shut itself off after a certain amount of time after the ignition is turned off.

So no need for elaborate circuits!:)
 
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