Upgrading wires to prevent electrical fires...

[McBenz]

I've decided to upgrade my 35 amp alternator to a Bosch 55 amp on my 1965 230 sl. Also I am replacing the starting with the newer/smaller size starter from Bosch. I was advised here that it would be smart to upgrade the "red cloth wire" that goes from the starter to the alternator with an 8 AWG wire to handle the higher amps.

 I also obtained a new heavier gauge positive wire that goes directly from the starter to the POS side of battery. I'm trying to figure out which other wires seem to be of concern, in regards to failure and causing fires. I checked the wiring diagram and see where there is another "red cloth wire" that goes from the back of the alternator towards the old voltage regulator and then along the outer firewall into the passenger compartment. Says it goes to the "rotary light switch" first and then to the fuse panel. But as I tracked down the wires it looks like it goes to the back of the fuse panel first. (I'd think it should be going to the fuse panels first anyway, so not to fry the light switch directly...IMO)  I'm also checking and cleaning all the ground straps for piece of mind.

 So, not to have to go on a full replacement of the wiring harness, is there anything one should replace that at least minimizes electrical meltdown/fire chances? ??

[lpeterssen]

Dear McBenz

Cables to change:

1) T30 red cloth cable in the route ALTERNATOR to STARTER in gauge AWG-8
2) T30 red cloth cable in the route ALTERNATOR to cabin where it connects to MAIN LIGHT SWITCH, in size AWG-10 (it does not go as you mention to the fuse box directly, it goes from ALTERNATOR to MAIN LIGHT SWITCH)
3) T50 (Signal to starter selenoid) cable GRAY in size AWG 14 from IGNITION TUMBLER to STARTER SELENOID. IF your car is automatic the cable pases trough the PARKING/NEUTRAL safety switch In the firewall.
4) T30 cable going from STARTER to BATTERY.  That in thick GAUGE, AWG4 capable of handling 100A

Enjoy your time upgrading your harness.

Best regards
L.peterssen

If you want to keep your external voltage regulator that serves the alternator, put new cables between alternator to ext.voltage regulator. Those are three cables. One is red/blue, another is black and finally the third is brown. All is gauge AWG 16 or 18.

If you want to have better fiability (trouble free operation) KILL your external voltage regulator and use an ALRERNATOR internally regulated.  If that is the case extend the blue cable (charging light) that goes to external voltage regulator and  connect it to your new alternator directly.

Those are the most important things to update.

Best regards
L.peterssen

[doitwright]

I understand the purpose behind upgrading the wires to the higher amp starter but why to the light switch unless higher wattage lamps are to be used?

[McBenz]

Great, thanks so much L.peterssen for the guidance. I will go that route, as well as use the internally regulated alternator.

[lpeterssen]

I understand the purpose behind upgrading the wires to the higher amp starter but why to the light switch unless higher wattage lamps are to be used?

Dear doitright

The intention of changing the CLOTH CABLE T30 size 4mm2 to AWG10 (6mm2) is not only because it will provide a higher current Pass trough, which if no new loads are added will not be necessary, as you indicate; BUT MORE IMPORTANT because of cable aging. I mean the insulation Made of cloth and resin which protects the inner copper on this particular cable gets BRITTLE After 50 years and is almost impossible to say that insulation is OK on it all long it’s way in the wiring harness.

As T30 cables are energized all the time, is CRITICAL to have PERFECT insulation, if not, apart from risk of fire, (since these are cables which are not fused on any part) we will observe high discharge rates on the battery.  That, reduces of course its lifetime, apart from generating more demand from other old parts of the system.

Best regards
L.peterssen

[doitwright]

Aging cables and wiring. Something to be closely examined when restoring a car. I will take a look at my harness as I make the electrical connections.

[lpeterssen]

Dear doitright

Yes, check your cables.  Specially T30 cable from alternator to starter and then to main light switch.

And the other always bad cable is the T50 starter selenoid signaling cable.  Route ignition tumbler/starter selenoid.The outer insulation of the copper core becomes extremely soft and breaks in many parts. That is a gray cable on the MB pagodas.

All the cables mentioned above should be changed from one terminal to the other.  Do not make intermediate soldered joints or joints of any kind, since these are lines which are not fused.

Enjoy that restoration and any question that may arise write me per PM.

Best regards
L.peterssen