I have the slow start issue with my GL450, read all of the comments, replaced my battery and starter, but the slow start is still happening. I have replaced the secondary chain tensioners on left and right and installed a check valve in the oil supply bore of each secondary chain tensioner in the cylinder head on left and right (TSB LI05.10-P-056435), and it still makes the same rattling noise on start up, so now I have the slow start issue and rattling noise going on. At my expense the car has had a complete wiring replacement by the dealership ($15k) so I can't imagine it being a bad cable. I replaced Left CV Axle Shaft Assembly, lower radiator hose, expansion tank cap replaced, replaced the front and back suspension systems (compressors, spring kits, shocks, etc), replaced motor mounts on both sides, and probably several other issues I haven't mentioned. I was hoping to work out all of the bugs and give the car to my son, but now all I want to do is fix the current 2 issues and get rid of the car. Yes, it is a great ride, but it is a real lemon. My first and last Mercedes!

 

2015 ... wrong forum

Sorry about all your troubles.

 

For anyone worried about the primary battery cable: There is one inside the engine compartment. It goes from the firewall terminal (under the red cap, for jump starting or trickle charging) down to the alternator and then on to the starter. It seems like the section of the wire from the terminal to the alternator gets corroded inside because it is not sealed and it is continuously conducting the full steady load of the motor, upwards of 50A.

Measure the voltage between the alternator positive lug and the terminal when the motor is running. You should only see a minimal voltage drop. I saw 0.5-1V, which on a 12V system is a huge loss. The alternator terminal was getting hot. Low charging voltage means the battery is routinely stressed.

Rather than replacing the whole cable, I just sistered a cable to the original from the alternator up to the terminal. This fit perfectly and left me with a spare. I got 4 gauge but since I was sistering I probably could have gotten away with 6 ga. $27.

The cable from the firewall terminal to the battery might sometimes need to be replaced, but maybe not, as those connectors are not exposed to the environment like the one on the alternator. Corrosion is the problem here.

 

thank you for this recommendation. It helped fix my slow cranking issue and battery draining issues. I bought the cable off Amazon like you recommended. I’ll attach some photos of it “sistered” to the existing wires. Like most people on this thread, I’ve replaced the battery and the starter and the problem persisted. This cheap cable fixed it and took less time to install than a battery or starter replacement.

 

Glad it worked out for you. You might want to sister it the full length, so as to not have loops of primary cable, vulnerable, as you have it. Also be very careful of any possibility of the cable rubbing on the body. Try to imagine the engine wiggling around - which it can. You also can get wire loom, which is already on the existing primary cable and acts as a secondary protection (but is mostly aesthetic).

Good job; glad it saved you.

 

Either the car was trashed by the previous owner,, or your dealer took you for a ride.
Who the hell replaces the complete wiring?

 

ok thank you for the further recommendations. I will get some wire loom and try and sister it the full length to make this more of a cosmetically and functionally better repair. Great idea. Thanks again as I thought your post on how to repair was the best so far. You must have some proper electrical training! I’ll try to post another photo when I get the loom.

 

Thanks, just trying to help, and glad it did.

Note I would post a picture with the loom - I have some available - but I haven't bothered! The cobbler's son walks barefoot.

 

If the suspect is the crimp connector at the starter, why not just cut the wire back a few inches and splice on a new (water proofed) end.

 

It is a pass-through connector. Double-ended at the alternator; one end goes up to the firewall post (to the battery) and the other goes on to the starter.

The suspect connector is the battery (or both) sides of the pass-through connector. One could cut off one side of the pass-through and put on a new connector; I don't have a crimper capable of 4 gauge wire, and I suspect the factory connections are soldered inside because I do not see any evidence of crimping. Maybe a screw down type connector, like what you see in breaker panels, would be available. It is so simple just to sister a cable though.

 

If I had to I might use a screw down connector or probably just solder the free ends, and tape and heat-shrink.

Most "Factory" connections are crimped, using a full circle die, so you don't see typically crimp marks.
It is easy for water to get in side and with dissimilar metals and a constant current, corrosion is inevitable.
I would think the terminal at the battery end is the easiest to replace, but also not likely to be corroded as it is protected form water.

 

There are obviously the connections at the battery, and a junction at the firewall post. I should check for voltage all the way from the alternator terminal to the battery positive.

I believe the connectors are copper, as is the wire, so there should not be dissimilar metal corrosion, but even plain old copper will build up oxidation when 50+ amps is going through the connection in the hot and harsh environment of the motor. Road salt would speed that as well.

Funny: I observed the resistance problem with a FLIR in the first place. Yes, the lug at the back of the alternator was hot. This probably contributes to failure of the voltage regulator. Losing one volt in contact resistance, at 50 amps, would be a whopping 250 watts to be dissipated at that one point. No kidding it gets hot. The only blessing is that both the lug and the wire are copper, so heat is conducted away very well.

Assuming the heating is caused by contact oxidation, the heat released would lead to additional oxidation ...

I don't know how common this sort of thing ordinarily is, but the GL was the first I'd heard of it.

I think I know the crimping die you are talking about. You basically jam the connector, with the wire inside, through a hole in steel that is smaller than the initial connector diameter.

If I had tried to repair the cable, I would have drilled a hole in the side of the lug and melted solder in. But I couldn't do that because it is a pass-through connector and couldn't get it out and clear to get a torch and solder in there.

FYI, since you like doing this kind of stuff, self-fusing tape is an excellent alternative to heat shrink, especially when you are not starting with a break in the wire.