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Premium Member 2018 SLC43
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2,847 Posts
Discussion Starter #21
The supplied cable with ring terminal ends + and - connects straight on to the battery 10mm bolts of the possitive and negative terminals .

Then so called routed through battery compartment neat tidy finish no cables showing as such .

This one was a 171 model fitment .
I agree fitting the CTEK Comfort lead directly to the battery is a good option:

But My R172 is tight up again the garage wall, so the O/S of the car is a lot easier to access.
Plus I drape the mains lead over the drivers door mirror, especially if parked outside, so I don't drive off with the CTEK charger still connected..!!! :surprise:
 

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Registered 2009 SLK200
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5,099 Posts
I agree fitting the CTEK Comfort lead directly to the battery is a good option:

But My R172 is tight up again the garage wall, so the O/S of the car is a lot easier to access.
Plus I drape the mains lead over the drivers door mirror, especially if parked outside, so I don't drive off with the CTEK charger still connected..!!! :surprise:
Or the simplest thing which i have done is connect direct to battery and purchase ctek extension lead plug and have the connection point at lower front of bumper / grille point area .

So no requirment to open bonnet and connect and can have it on the n / s or o / s front of vehicle .
 

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Premium Member 2014 SLK200
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2,478 Posts
Or the simplest thing which i have done is connect direct to battery and purchase ctek extension lead plug and have the connection point at lower front of bumper / grille point area .

So no requirment to open bonnet and connect and can have it on the n / s or o / s front of vehicle .
Yup, nice convenient space hidden behind the number plate here in the UK:wink:
 

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Premium Member 2018 SLC43
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2,847 Posts
Discussion Starter #24
R172 CTEK Install - Part Two:

OK, bit of a delay from starting this Post, but here is the Install of a "CTEK Comfort Indicator" Lead on My RHD R172.

The advantage of one of these leads is it’s fused which is somewhat important when connecting to a car battery (especially outside of the battery compartment) that can dish out over 600 Amps... But the Lead also shows at a quick glance when under the bonnet (Hood, for US readers!) the battery status & whether the battery is charging once the engine is fired up :tu:

This is what comes in the box as they say and is a good quality item:



But always room for improved, so I have covered the cable in some Braid Protection that not only gives the lead a bit more “body”, but also helps it to blend in, in the engine compartment:



This is the lead ready to install, though I would have preferred to put the CTEK Lead under the existing lead on Terminal (3) for a more covert install, I was a bit worried about how much current might go through this lead..
So decided to take @Windinmyhair advice and just use a washer and nut on top of the existing nut. Plus to use the Frame Earth (5) along with two washers (only one washer shown in picture) under the existing nut.



At this point I will High Light Safety, when working with electrics....
Ideally the main battery should be disconnected before carrying out any work on the car electrics, as any spanner will just vaporise into molten metal if You short out the jump point to earth...!!

Here I have used a cleaning cloth to reduce the risk of an accidental short & was wearing glasses:



Close up of the CTEK Lead installed and just a bit of black permanent pen to give a more covert install.
Plus I put an additional bit of sticky cloth tape where the lead passed under the black metal frame, just in case it ever rubbed and also black sticky tape around the last bit of bear red cable:



With the final touch of a cable tie around the bonnet release cable to hold the CTEK lead in the correct position, this was the final result:



Just a final point, while installing the Lead I measured the current used by the CTEK Indicator Lead at less than 2 mA, so will use up 50% of a fully charged battery after about 2 years, if the car is not used & battery is not charged..!! :nerd:
 

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Registered 2009 SLK200
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5,099 Posts
I've got a neater solution to that one. I'll share it once I've got it done.........
Note : the ctek end has got a rubberised sealent end cap but no harm in playing it safe especially with uk roads and gritting etc .
 

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Registered 2013 SLK250
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12 Posts
Once again I thank everyone for the great comments and solutions. All seem to work in each individual application. On my R172 there does not seem to be enough thread to even use a halfnut on terminal 3. So it only seems logical to me to attach the + ring terminal from the battery tender to terminal 4, since it is not used at all. The ease of access to this terminal overrides access to anything else, including the battery. My only question at this point is whether terminal 4 is OK to use for this application.
 

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Registered 2009 SLK200
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5,099 Posts
I'm intrigued! :laugh:
Not tried it but possible the extended ctek end connection can be accessed via the tow eye location flap on the 171 and poss 172 models ?
 

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Premium Member 2018 SLC43
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2,847 Posts
Discussion Starter #31
~~ On my R172 there does not seem to be enough thread to even use a halfnut on terminal 3. So it only seems logical to me to attach the + ring terminal from the battery tender to terminal 4, since it is not used at all. The ease of access to this terminal overrides access to anything else, including the battery. My only question at this point is whether terminal 4 is OK to use for this application.
Re: Missing lead on Terminal "4" - So do You have heated seats & Airscarf in Your SLK?

I couldn't see any difference in voltage between Terminal "3" & "4" so in theory I guess it can be used... Need someone with access to the MB wiring diagram for this module to understand what is going on :nerd:

Be interesting to see a close up picture of Terminal "3" on Your SLK's jump point?
The other way is to take the existing nut off Terminal "3" and put the CTEK eyelet under that nut? (With a washer on top of the CTEK eyelet)

I just used a regular 4mm high nut + washer that "just" fitted under the cover...!!
Luckily I have a container of old nuts & bolts in the garage, so had a choice or what type of nut to use:

 

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Registered 2013 SLK250
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12 Posts
Trev5, Great pictures. Wish I could say the same for mine, but you can see that terminal 4 is complete blank. The car does have the P01 option with Airscarf and heated seats. It is a little difficult to see that terminal 3 is loaded up to where there is only 1 thread exposed, hence the desire to attach to terminal 4. But you are probable correct is saying that the only definitive way to determine if this is a good way to go is getting input from a source that has access to the wiring diagram.
 

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Premium Member 2015 SLK55 AMG
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96 Posts
Any idea what terminal 1 is for in Trev's pictures?

I have just connected a CTEK comfort connector there as it seemed the most accessible. I checked the voltage on the three terminals, 1, 3 and 4 in your picture, before adding the comfort connector, and they were all the same. 11.84 volts

However, once I connected to terminal 1 (removed bolt, added comfort wiring) I checked the voltage and there was nothing there. Terminal 3 and 4 voltages were same as before.
Restarted the car and checked with the engine running and all three were the same. 14.9 volts. Turned off the engine and checked, all three were the same once again.

Slightly confused, so I checked everything was working in the car and all the electrics were fine. So I bit the bullet and connected the charger (CTEK Time to Go) and it seems to be charging OK, all lights as they should be.

I just wondered what each of the three terminals are actually used for, and whether I should switch to one of the others.
 

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Premium Member 2018 SLC43
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2,847 Posts
Discussion Starter #34
@Rv8 - 11.84 volts is low...!!
I've not read exactly what the fall function of the Terminal 1-4 Jump Point does - Except that if will disconnect power to stuff in the event of a frontal crash (Part of the Air-Bag system, which sounds a good idea..!!)
I also found all terminals had exactly the same voltage... I didn't risk removing any cables, as the car was still under warranty - Though struggled to trace where the cables went to, from this Jump Start Point:

Though interesting that removing the cable from Terminal 1 showed that it was a incoming voltage cable?
...but the voltage on Terminal 3 & 4 stayed the same..

Need someone to source a R172 wiring schematic diagram for this area (y)
 

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Premium Member 2015 SLK55 AMG
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96 Posts
@Rv8 - 11.84 volts is low...!!
I've not read exactly what the fall function of the Terminal 1-4 Jump Point does - Except that if will disconnect power to stuff in the event of a frontal crash (Part of the Air-Bag system, which sounds a good idea..!!)
I also found all terminals had exactly the same voltage... I didn't risk removing any cables, as the car was still under warranty - Though struggled to trace where the cables went to, from this Jump Start Point:

Though interesting that removing the cable from Terminal 1 showed that it was a incoming voltage cable?
...but the voltage on Terminal 3 & 4 stayed the same..

Need someone to source a R172 wiring schematic diagram for this area (y)
Thanks Trev, I’ll maybe disconnect it again just to check whether this is 12 volts at the terminal or the cable.

Peculiar that there was 12v before I started though, but not when I’d finished.
 

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Premium Member 2015 SLK55 AMG
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96 Posts
Thanks Trev, I’ll maybe disconnect it again just to check whether this is 12 volts at the terminal or the cable.

Peculiar that there was 12v before I started though, but not when I’d finished.
So, I have removed the comfort lead from Terminal 1 this morning.

Once I had removed the the cables from Terminal 1. I checked the voltage at the terminal, it was 11.8 volts, the same as the other two terminals.

It probably would have been OK, but I had a sleepless night wondering why the voltage disappeared when I first connected it there. It may have simply been a test lead not connecting properly, but for my own peace of mind I had to move it.

It now is connected to Terminal 3, right next to the main +ve charging point. I had to drill out the eyelet terminal connector slightly as it was too small for Terminal 3. Bolts were 10mm on Terminal 1, 14mm on Terminal 3.

Battery on charge as we speak.
 

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Premium Member 2015 SLK55 AMG
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96 Posts
OK. It has now been on charge all day, about ten hours, voltage now shows 12.22 volts at rest, it was 11.8v.

One thing though, when I locked the car the mirrors didn't fold in as usual, but that's hopefully just a menu option, possibly the smarttop options have changed.
I had disconnected the battery, so it's entirely possible that other things may have returned to default settings.

I'll check tomorrow.
 

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Premium Member 2012 SLK55 AMG
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7,009 Posts
I would have thought after 10 hours that should be nearer 12.8v. What CTEK charger do you have?
 

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Premium Member 2018 SLC43
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2,847 Posts
Discussion Starter #40
OK. It has now been on charge all day, about ten hours, voltage now shows 12.22 volts at rest, it was 11.8v.
11.8 volts was a very flat battery....

If Your SLK has not fully gone to sleep, it may well show 12.2 volts on a part charged battery.

The CTEK is a battery conditioner, not an old school battery charger. So if it needs to put 50Amps back in at 3 Amps/hour, till 80% - Then it may need a good 24 hours or more to fully charge the battery...?

Plus, I'm guessing that Your battery is original & 5 years old..??
 
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