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2005 E320 Wagon, 1987 560SL, 1983 380SL, 2008 QX56, 2004 BMW R1150GS Adventure
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Discussion Starter · #1 ·
Ok, so I thought I had sorted the mess behind the dash in my '83 380SL. Found a wiring diagram, traced the correct power/constant wires, hooked up an aftermarket digital receiver, powers up and saves settings as it should.

The issue is it seems to lacking enough juice. When I turn up the volume, the radio shuts down. If I keep the volume low, it is fine. A multimeter seems to show the switched power (which is a green/red wire) is a constant 12v. I put in new fuses, and can't seem to see any area where the wire is frayed or shorted.

Given that there is no wiring to the cig. lighter, and given the rest of the mess behind the dash I may have to go in deep - but wondered if anyone had any experience with finding power elsewhere, or words of warning on pulling the fuse panel out to trace and/or re-wire?

Thanks!
 

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'80 450SLC Afro RHD Ikonengold
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If you are to rewire your radio to anything else other than original wiring (for whatever reason), it is the best option to run wire/s directly from the battery (presumably your batt is in the engine compartment). That's positive AND negative. May not be as important to run negative for digital radio.

Get a thick wire, tap in by the batt terminal, a bit of cabletie and a fuse in line will be all that you need. Having inline filter (choke) can only help but should not be essential.

Most radios reset when there's insuficient current supply (as volts drop significantly)
 

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2005 E320 Wagon, 1987 560SL, 1983 380SL, 2008 QX56, 2004 BMW R1150GS Adventure
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Discussion Starter · #3 ·
If you are to rewire your radio to anything else other than original wiring (for whatever reason), it is the best option to run wire/s directly from the battery (presumably your batt is in the engine compartment). That's positive AND negative. May not be as important to run negative for digital radio.

Get a thick wire, tap in by the batt terminal, a bit of cabletie and a fuse in line will be all that you need. Having inline filter (choke) can only help but should not be essential.

Most radios reset when there's insuficient current supply (as volts drop significantly)

Thanks, thought about doing that. Battery is in the trunk, but I am going to re-wire a new antenna anyway. The only downside is having the radio on an unswitched circuit (and having to remember to power it off everytime I shut the car off). Should I put in a relay off a switched circuit or something?

Thanks again....
 

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1975 450SL
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2,440 Posts
There should be two circuits to the radio: one switched and one unswitched. You may be trying to run the whole thing off the unswitched side that is designed for low current "maintenance" type supply (clock, tuner memory, etc..). You may need to dig further into your diagrams for both the car and the new radio to find which wires should be connected where.

In the trunk-battery type vehicles, there is a connection point on the passenger side front fender that you can get high current, unswitched power from, if needed.

Keep the thread alive, and we'll help you out.

Scott
 

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2005 E320 Wagon, 1987 560SL, 1983 380SL, 2008 QX56, 2004 BMW R1150GS Adventure
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Discussion Starter · #5 ·
Hi Scott - according to the wiring diagram (and my multimeter) I have the correct wires connected (a red constant in the car connected to the yellow constant on the radio harness) and a red/green switched to the red switched on the harness, and a good ground. It saves the settings on the receiver, turns on correctly when I turn the key, but if I turn it up (or turn on the head lights...) it shuts down.

The wiring diagram shows the red/green switched wires going to the radio is coming off the cigar lighter, which is fed by a bk/yl/gn. There is no wiring to my cigar lighter at all, so I may start there by removing the ashtray (looks like after I remove the ashtray there is a bracket I remove?)

If that doesn't track it down I may just run it direct off the battery for now and see what I can do....

thanks!
 

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1989 560SL
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When I was having problems similar to yours, all my wires checked okay with my meter. Someone on this forum suggested a bad ground even though it checked out by meter and that turned out to be the problem. I rerouted a new ground wire and the radio works fine. Good luck.
 

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1975 450SL
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Ok, you've gotten the hard part taken care of; the wiring is correct. Now for the Fiendishly Difficult And Madness Inducing part: trying to find the problem. :D

The suggestion about checking your grounds is very good, but don't stop there, check all the connections involved. A connection may read 'good' with the low currents from a multimeter, but be poor at higher currents.

The most common failures are at the connectors themselves (loose, corroded, worn) then the wire itself (routed over a sharp edge, pinched, damaged). A telltale for corrosion is a greenish powder (copper oxide).

A supply of heat-shrink tubing and a heat gun is handy. You can even get terminals with heat shrink attached. The best is the tubing or terminals that are intended for automotive use that is filled with a type of hot-glue that creates a weather tight seal.

Sorry to "dump" info, I do that sometimes.:eek:

Scott
 

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Discussion Starter · #8 ·
Thanks.... yeah, all connections are clean - new cuts/strips, all the wires at the head end look good (solder and heat shrunk).

I am going to tap a new ground, and see what that does first, then try to run a power line from the battery and see what I get.

I know the radio is the least of my worries, but want to make sure the symptom is not indicative of some other issues I need to be looking at.....
 

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'80 450SLC Afro RHD Ikonengold
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Hi Scott - according to the wiring diagram (and my multimeter) I have the correct wires connected (a red constant in the car connected to the yellow constant on the radio harness) and a red/green switched to the red switched on the harness, and a good ground. It saves the settings on the receiver, turns on correctly when I turn the key, but if I turn it up (or turn on the head lights...) it shuts down.

The wiring diagram shows the red/green switched wires going to the radio is coming off the cigar lighter, which is fed by a bk/yl/gn. There is no wiring to my cigar lighter at all, so I may start there by removing the ashtray (looks like after I remove the ashtray there is a bracket I remove?)

If that doesn't track it down I may just run it direct off the battery for now and see what I can do....

thanks!
I've repaired many a car radios (up till 4 years ago) and I have never seen a yellow wire that was (a constant) power supply feed.
Yellow wire was always an auxilary device power output (like antena or power amp start etc).
I do not say it is not possible, just doublecheck that you're not feeding the power wrong way round (and it is possible for radio to run like this and with errors like yours).
 

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2005 E320 Wagon, 1987 560SL, 1983 380SL, 2008 QX56, 2004 BMW R1150GS Adventure
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Discussion Starter · #10 ·
I've repaired many a car radios (up till 4 years ago) and I have never seen a yellow wire that was (a constant) power supply feed.
Yellow wire was always an auxilary device power output (like antena or power amp start etc).
I do not say it is not possible, just doublecheck that you're not feeding the power wrong way round (and it is possible for radio to run like this and with errors like yours).

Definitely yellow on the harness (Kenwood, but most are similar).

It actually had to be reversed on my wife's e-class for the same radio/harness (which plugged into a pre-made harness). On most aftermarket radios, the red is switched, yellow is hot full time (or at least most I have installed). (Most I have seen have a Blue antenna trigger wire)

Thanks, though... gonna play with it tomorrow. I'll get it whipped.
 

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'80 450SLC Afro RHD Ikonengold
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Well, a simple way of checking a sufficient current supply is with a multimetre (Volts).

Measure constant power wire relative to the ground anywhere in the car (not the radio case) and if it drops with volume, you have the culprit.
For ground checkup, measure volts between the ground anywhere in the car and radio case. Anything more than few miliVolts is a sign of poor ground.
Elsewise, you may have a faulty radio in deed
 

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Discussion Starter · #12 ·
Well, a simple way of checking a sufficient current supply is with a multimetre (Volts).

Measure constant power wire relative to the ground anywhere in the car (not the radio case) and if it drops with volume, you have the culprit.
For ground checkup, measure volts between the ground anywhere in the car and radio case. Anything more than few miliVolts is a sign of poor ground.
Elsewise, you may have a faulty radio in deed

Thanks! Ruled out the radio quick (Plugged the one from my wife's car, and another we had). Definitely the wiring in the car - but the car may be a bit of a basket case. I was/am more worried about this being endemic of what is to come as I tear into it. Ah well... I have beer, a fire extinguisher and tomorrow looks like a nice day!
 

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Discussion Starter · #13 ·
I know everyone has been unable sleep until the noob gets his radio working, so rest easy, was an intermittent ground issue.... (tested with a new wire run to the battery). So rest easy now....

I ordered a new antenna and new antenna cable, so going to wait for that to arrive then I can run a new ground cable along with the trunk and just go direct to the battery.... thanks for the help!
 
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