Burned alternator wires

[mbazinet]

Hi Folks getting a bit deeper in to inspecting my dads 66" 230SL  seems at some point 3 wires from the alternator got so hot the insulation has burned off exposing the bare wires   about 3-4 inches worth directly from the alternator.

I don't trust my trying to repair 50 year old wiring just to create additional problems with reliability,  I'd like to replace the harness , any vendors I can go to to purchase a new harness and do a proper job ?

[ja17]

Rhode Island Wiring has always worked for me.

[Tyler S]

That is a very common place for the harness to overheat. It is only a 10 gauge feed wire to the battery. It runs from the back of the alternator down to the connection terminal mounted on the oil pan. Then it goes to the B+ lug of the starter motor. Cloth covered. When it gets hot it can take out the "3" smaller wires that run to the voltage regulator and starter solenoid. These split off about 12 inches from the alt connection. Its a pain to get to but can be done. Do yourself and your car a favor and replace the 10 gauge with 8 gauge wire. Also a good idea for those of you who want to or have installed an upgraded amperage alternator.  Will minimize potential for a fire.

[mbazinet]

Joe  with the folks at RIW   what would I ask them for ? Full harness or a specialty harness?

Thanks !

[mbazinet]

What condition would cause this harness to overheat ,  this does not seem like MB quality   this seems to be a more like British Leyland ?

[Tyler S]

A car that has a dead battery or shorted battery cell will cause this to overheat. 10 ga wire is only good for 30 amps. The stock alternator will put out up to 35 amps with demand such as a dead battery or a huge stereo system etc...
This is the "bottleneck" in the system.
Mine had melted to the point that the wire was exposed and all it would need is a short to ground to start a fire.
Later cars (107 and sedans) had substantially larger alt wiring.
This is something EVERYONE should check on their cars. It is very hard to see under the manifold, and with dirt and grime on the harness as well as the black sheathing can hide what is going on underneath.
Replacing the entire engine compartment harness is a big job. Instead, If you dont want any splices you can slice open the existing harness from the alternator to the voltage regulator and replace the wiring.
I replaced the sub-harness from the oil pan connector to the starter lug with a newer part from a sedan. Identical except for the larger feed wire.
Also replaced the culprit 10 ga wire from the alternator to oil pan terminal with 8 ga.

[Tyler S]

A few more pics for post above

[mbazinet]

Thank you very much Tyler those pics are very helpful the description is spot on you'd hardly notice it unless you were doing a thorough inspection.
So much grime it could be mistaken for black insulation.
I see that the battery was not strapped down and I see arching on the inside of the hood above the posts .  Now that I know I'm pretty sure that's what caused it , my dads not very mechanical.  Not that she is mine I'll change all that !

[mbazinet]

Today I decided to tackle the burned alternator wire harness. Over the weekend the charging light came on and looks like the voltage regulator has gone bad  I elected to change that with the OEM  as well as the rebuilt Bosch alternator while I had everything apart

Attached are pics of the wires after I removed them from the harness, you will see the overheating damage that was a "ticking time bomb"   all will be corrected in a few days.   I will post a few pics of the repaired harness.

[mbazinet]

Today I repaired the burned wires and replaced all of the alternator and starter wiring harness damaged sections.
Although not standard MB wires and such I am very happy with the outcome, I have a new alternator and Voltage regulator on the way I expect to be back in business  in a few days   thought you all may like to see the finished product :

[Tyler S]

Lookin good 

[mbazinet]

As recommended I used 8 gauge wire for the 2 primary leads as an upgrade.   I hope that this may stop some of the problems related to the stock 10 gauge wire overheating during normal operation. All connection terminals (covered with heat-shrinked harness)  I used Marine Grade Crimp Terminals  all heat sealed. Hoping it will hold up well.

Thank you for the nice comments I will report back soon as she is running .
 

[mbazinet]

Happy to report the car is now back on the road ! While I had it all apart I changed out the starter with a rebuilt Bosch unit.  I was surprised that all the procedures for the starter change  indicated I would need to either go through the trans tunnel access cover or use a 3ft. extension to gain access to the top allen bolt. it turns out not necessary,  very easy access from bell-housing with the car up on the lift. Could be my imagination but the car seems to run much better with the repaired harness and alternator..