'86 300SDL Radio Install. Only works with door open! - PeachParts Mercedes-Benz Forum

hawkXcore · #1 08-29-2009, 03:48 PM

Hello ladies and gentlemen, I've been lurking here for a few weeks since I got my 300SDL, and figured it was about time to post. I wired in a new Sony headunit to my car, with one problem. Since the install, the dome light only comes on with the key in the ignition, and the radio only works with key on and the door open. I searched, and found someone with a similar problem, traced back to the Power Seat Diode. I went to Radio Shack today and purchased a replacement 1N4003 diode, and soldered it into the factory holder in the fuse box. Popped it in hoping to hear the radio turn on. No such luck. I'm now out of ideas... seems the factory diode was working just fine. Any ideas?

Jeremy5848 · #2 08-29-2009, 04:06 PM

Being a clever fellow, you would never wire the replacement diode in backwards, right? You might also check the wiring to the (should be) two switches in the driver's door A-pillar. One switch turns on the dome light (and does other things) while the other turns on a relay that allows the power seats to be adjusted before getting into the car and turning on the ignition. The relay should be in the fuse/relay box under the hood but I don't know exactly where as I'm unfamiliar with S-class wiring. It almost sounds as if you wired the radio into the wrong power lead. What radio did you remove to install the Sony? Was it the original factory radio or another aftermarket?

hawkXcore · #3 08-29-2009, 04:16 PM

Quote:

Originally Posted by Jeremy5848

Being a clever fellow, you would never wire the replacement diode in backwards, right? You might also check the wiring to the (should be) two switches in the driver's door A-pillar. One switch turns on the dome light (and does other things) while the other turns on a relay that allows the power seats to be adjusted before getting into the car and turning on the ignition. The relay should be in the fuse/relay box under the hood but I don't know exactly where as I'm unfamiliar with S-class wiring. It almost sounds as if you wired the radio into the wrong power lead. What radio did you remove to install the Sony? Was it the original factory radio or another aftermarket?

Jeremy,
First of all, thank you for your help. According to the wiring diagram, the diode should flow to pin 1, which from what I remember from electronics class way back when, the side of the diode with the stripe on it is the side it flows to. So in that case, to my knowledge, yes it's wired right. Between my original post and your reply I actually went out to the car and switched the wires going to the door switches to rule them out. Same problem. As far as the relay, I'll have to check it when I get home... I don't have my ETM cd's at work with me. I don't believe I wired it to the wrong lead, I just think there's something screwy upstream. I used the diagram directly from the ETM, and wired to the Sony diagram. I removed the factory Becker Grand Prix radio to install this. But, I guess I should add something. When I was cutting the factory harness, I was a little hasty. I cut the entire pack of 4 wires (hot, ignition, and the 2 illumination wires) in one cut. Yes, there was an arc. Yes, I'm an idiot. That's why I assumed that I may have popped that diode, especially considering it's a known problem. Now, would a very small split second arc have carried enough amperage to blow a relay? I'm not sure...

hawkXcore · #4 08-29-2009, 04:19 PM

Oh, also let me correct myself. I did NOT wire to the Sony diagram. I lost my instruction manual long ago. I wired to the universal aftermarket diagram I found on the12volt.com. I'm 99.9% sure it's correct lol. Even still, I put a test light to the harness coming from the factory. The proper wires are NOT hot at the proper times. So even if I wired the deck wrong, it's still not getting power when it should.

Jeremy5848 · #5 09-01-2009, 01:57 AM

I'll bet you popped a fuse or blew a relay when you cut the wires in one swell foop. Mercedes occasionally put extra fuses here and there and some of them are hard to find if you aren't expecting them. I would like to be more specific but I just don't know much about the S-class electrical systems. There is a fuse in most Becker radios but that would have been removed with the radio.

Let's take your statements one at a time and see if I can help. You said "the dome light only comes on with the key in the ignition." Do you mean that literally, key in the ignition but not turned to any of the "positions?" There is a "key in the ignition" switch that sets off a buzzer if you try to get out of the car without taking the key.

If the dome light is being triggered by "key in ignition" while the radio works only with the door open (and key on) then I would say that one or more wires are crossed or a "convenience" relay is blown. The "convenience" relays have electronic components (timers and other things) that could be blown by a short-circuit. There are so many interconnected circuits in Mercedes wiring and the "higher class" cars have more of it.

If you cannot come up with an "aha!" moment, I would recommend trying to put the wiring back to stock as much as you can in the hope that by so doing you will find the underlying problem. Sorry I don't know more about S-class wiring.

Jeremy

ah-kay · #6 09-01-2009, 02:42 AM

The 4 wires you cut should be as follow. Use a meter to measure them. I cannot remember the color of the wire off-hand.

1) 1 wire is constant 12V to remember radio setting with key is off
2) 1 wire is switched 12V when key is in posn 2 to turn radio on
3) 1 wire is switched variable 12V when parking light is on for dimming.
4) 1 wire is ground.

Once you identify these 4 wires then wiring the radio is a piece of cake as they are all the same. The diode may be a red herring as I don't even know it exists. Hope this help and good luck.

Jeremy5848 · #7 09-01-2009, 12:09 PM

There is also a wire carrying switched 12 volts for the power antenna but that probably is in a separate connector and in any case is a load rather than a source.