Author Topic: A couple of electrical questions...  (Read 1910 times)

Andrew280SEL

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A couple of electrical questions...
« on: 20 August 2006, 02:23 AM »
Hi there

I have a couple of electrical questions I hope you experts can help me with.

1. When I installed my CD player I had to find a constant 12V for the memory wire as there wasnt one already there. My original idea was to run a wire out direct to the battery. Simple...no not really. I couldnt work out how to get out of the car! By which I mean getting the wire through the dash and out the firewall to the battery. These things are tanks! So eventually I hijacked the hazard light switch circuit. It works of course, but I still want to run one out the to the battery. So any tips on escaping these impenatrable tanks? Cos I have no idea what route to take to get the wire out past everything...

2. My tacho has never worked since I bought it. I havent taken it apart to look at it, but would it be whatever drives the actual needle or do you think it's simply wiring? I'm not sure how long these last so im just after ideas before i go searching into the unknown...

3. Another CD player problem. While I was searching for a constant 12V supply, I played around with the electrical tester to see if everything else was right (like if the earth was good, accessory power lead etc) and all was good. I wire it all up, shove the player in, turn the key....nothing. I took the player back out undid my connections and checked everything again. For some reason the accessory power (red) lead is no longer supplying current. It always was before, but all of a sudden its not. Now admittedly, that wire comes out of the same harness that the earth (brown) lead comes from, and when I tried to strip the earth lead I had more trouble than usual and yanked it a little hard... so perhaps its just come loose through my foolishness. Would this wire go directly to the ignition switch? If so would it be reasonably easy to remove and fix? I know I should probably go and explore but I'm a bit scared to pull this car apart to much. I ended up for the time being hooking the cd player power lead to the glove box light lead just so i can listen while driving.

Any help whatsoever will be much appreciated!  ;D

Thanks in advance
« Last Edit: 20 August 2006, 02:47 AM by Andrew280SEL »
'79 280SEL- 560,000 Kms
'73 350SE- getting an AMG facelift
'79 450SEL 6.9

Des

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Re: A couple of electrical questions...
« Reply #1 on: 20 August 2006, 04:15 AM »
I'm no sparkie but just some thoughts....


Wouldn't the clock have a constant 12v going to that?
Have you tried traceing that back to where it comes from and then running another set of wire(s) from there?


Good to see another Tasmanian member on the board.

 ;D Des

1977 W123 230 
1977 W116 280S *new*
1980 W123 250
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oscar

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Re: A couple of electrical questions...
« Reply #2 on: 20 August 2006, 05:44 AM »
Hi andrew,

Have you checked this thread out for some details on the tacho?  It was fairly recent and some good info.
http://forum.w116.org/index.php/topic,648.0.html

There's a few round multiholed grommets in the firewall where you could run a wire from the battery straight to the radio.  You'll have to remove the below-the-dash kickpanels to feed the wire thru.  As far as schematics and what fuses to use etc I'm no sparky either unfortunately but for pics of a good install check jjccp's installation thread.
http://forum.w116.org/index.php/topic,558.0.html

Good luck.  With the first cheap radio from Autobarn that I bought so I could get FM, I didn't realise you needed a memory wire, so it became a PITA to search for a channel every time I started the car.  To top it off, after a week or so, smoke started coming from the middle console as the radio shat itself.  Cheap radio or my expertise??
1973 350SE, my first & fave

Andrew280SEL

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Re: A couple of electrical questions...
« Reply #3 on: 21 August 2006, 03:01 AM »
Thanks a million Des and Oscar. I'll take it on board. Now I just gotta get some spare time . Maybe the weekend i guess.
(by the way Des, we would probably be the only two Tasmanians here wouldnt we? ;D)

I did think of the clock, but i wasnt sure of going that far at that time. So i just hooked the wire to the hazard switch which is really close by. But I think Ill try to get the wire to the battery eventually.  I suppose I could also hook my Power lead to a constant supply too, but Im not sure thats a great idea or not. It could run all the time and flatten my battery, but at least i could use it when parked as my accessory power lead is dead. Anyway, ill see.
As for the tacho, ill deal with that when i remove the steering wheel (my current one has suspicious chew marks and a huge chunk taken out. Ive got a good one from a donar car though) so then will be a convenient time i think to check the tacho. It could just be a wire disconnected from the coil of course...
Anyhow, just gotta wait to the weekend.

Thanks again
'79 280SEL- 560,000 Kms
'73 350SE- getting an AMG facelift
'79 450SEL 6.9

cipha

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Re: A couple of electrical questions...
« Reply #4 on: 23 August 2006, 10:15 PM »
When fitting a newer sound system there are just a few things of which one should be aware.

1. Get a really good earth point.  I made a new earth strap up and put an eyelet at one end, which was then secured to the bodywork by the gear selector lever.  Undo one of the bolts and pass it throught the eyelet.  Using a voltmeter one should check to see that there is not have less than 12 volts across this: any less will see a modern unit switch itself on and off or not work properly.

2. For an unswitched 12V line the clock line is OK for the memory function: just be sure to put a low value fuse in line for safety sake. 

3. More powerful radios and amplifiers really need a solid bit of iron to suck out the Amps for the 'main input' power feed.  Fit a wire direct to the battery and pass the line through the fuse box and back through the body work following the factory wireing.  If you are less enthusiastic and don't want to go to this effort, then make a new passage via the rubber grommet adjacent to the fusebox: you'll find air lines and other items going through here.

To connect into the existing MB wiring looms, for speakers etc, go to a hardware store and buy the 'strip' connectors which allow for one to screw down onto the wire.  Set this up with the radio side first and then carefully join one item at a time from the existing items - speakers, antanna switch etc.