small wiring confusion

[olliparr]

280se 1977.....Just put a new radio in. Checked the wiring diagrams as available online. I was always under the impression that the radio ran off the cigar lighter - however, according to my reading of the wiring, the cigar lighter is on the the wrong side of an earth for the radio. On the diagram the radio gets power from the ignition circuit with an inline 2amp fuse - but when I opened the inline fuse I found not a 2 but a 25amp fuse....Has some previous owner been fiddling here? Did the original radio not run off the cigar lighter? Did the original Becker only run off a switched power source and no continuous? Can anybody enlighten me...?

[Bandolero]

When I changed the radios in my 79 280SE and 78 450 to modern cd players, I used the earth wire (light brown) off the cigar lighter and the memory wire I connected to the power wire of the hazard switch.
The original power wire to the radio is red with a light brown line in it. This wire is in the same lume as the cigar lighter wires but not connected to the lighter. (Please check with a multimeter as I don't want to be held responsible for any problems.)
Also, if the radio is a modern one with its own fader incorporated in the system you CAN'T use the original fader as you will blow the stereo up. (At least that is what the retailer told me.)
As i don't like excess wiring etc on a car that does nothing, I removed the original fader switch and filled the hole with a small piece of wood. Then I placed a bit off velcro over the spot and put some more velcro on my mobile phone and it is a perfect spot to have the phone sitting on the console. Very neat. Now the phone doesn't move when I'm doing high-speed cornering in the 280. (Only joking)

[olliparr]

Thanks for that - I checked the lume going to the cigar lighter and I have two light brown (earth) wires, and one black wire with a yellow stripe.....which has current, but runs I think from the 25amp fuse number 6 in the box. Any ideas on the inline fuse?

[Bandolero]

I just used the in-line fuse that came with the radio. However, mine was a modern one.
If you are using the original radio/cassette you may have to put an in-line fuse into the system.
Is there another spare wire in the radio area of your car? If so, check with a multimeter as I am not sure if the cigar lighter works on ACC or Ign. If it is only Ign, it would be better to use a wire connected to Acc as it would be no good leaving the motor off but on Ign so that you can listen to the radio.
I can't remember if there is an extra wire available. (I'm old and forgetful)

[BAR]

Another point worth noting: Having had this problem myself.  Do check that your earth is GOOD.  Modern radios need a good earth: so check, with the aid of a digital voltmeter, that you have more than 12 V across your main power [and also switched power] feed to the earth wire.

As a precaution, simply add in a new earth wire from the radio to the chassis using one of the gear selector indicator's mounting points.

[Bandolero]

Hi Ollipar,
I just checked a 450SEL I am wrecking to make sure I didn't "lead you up the garden path.)
That saying sure shows my age!!!!!!!!!
In the lume to the lighter, there is a black wire with a brown or green line. This power wire goes to the lighter plug. Then there are 2 light brown wires (earth), one goes to the lighter plug and the other one (on the 450 I am wrecking) goes to the earth on the radio. Then in the lume, but not connected to the plug is the radio wire which is red with a light brown or green line in it. This wire works on ACC as well as IGN, but the lighter wire only works on IGN. Check the 2 brown earth wires and see if one is able to be pulled out of the lume (gently), as someone may have stuffed it into it to get it out of the way.
Bar is right, if you can't find the earth, just feed it through the console and connect it to one of the bolts on the gear selector.
Good luck finding the ACC wire as that will save you heaps of hassles.
PS: Don't forget to add the memory wire to the hazzard switch and also I think the automatic aerial wire is blue.

[olliparr]

Thanks again - the red radio wire just isn't there - whoever took the original radio out made a bit of a mess in there leaving plenty of multicoloured loose ends - I've got good earths however. The backlights on my automatic shift have gone out now, so I think its time to get the console off to have a proper look...