Guys I have an issue that I could use some help on. I'm rebuilding my 1973 914-4 wiring harness using AWG GXL wire. I have a schematic for a 1973 but the wire size, in MM's, is not shown. I found, on the forum, a file called "914_Electric_74_Current Flow (partial copy of that file is attached). In matching it to my harness I found a major issue, IMHO.

Of the four Red wires coming from the Battery - two are noted as 2.5MM (10/12 gauge wire) and two as 4.0MM (these 4.0MM wires (6 gauge) go to the ignition switch and the other to Fuse 11).

My question is this a typo / I'm reading it wrong because I do not have a 4.0MM wire, in my old harness, going to the Ignition Switch and Fuse 11, all four wires are 2.5MM or 10/12 gauge AWG wire.

Second question, if I have room for 10 gauge in the center tunnel should I run 10 vs 12 gauge just to be safe? GXL wire has a thinner sheathing compared to old PVC wire that I'm replacing.

Norm
Click to view attachment

It's all about voltage drop. The GXL wire you're using is way beyond what the factory used so a 12awg is probably more than enough.

Here is a small paper I put together back when I was making fuse block mods for the 914. There are 2 (2,5 mm) wire and 3 (4,0mm) wires. These wires are very high stranded wires. One of them, I am not sure any more, had 56 strands. I believe it was the 4.0mm. This high strand count allows greater flexibility. I always was under the impression higher strand count had better current carrying capacity, but that is only for AC higher frequency applications, so I apologize for any misunderstand I may have created.
If your car did not have 4.0mm going to the front of the car to the fuse panel and ignition switch, maybe someone changed them out at some point.
I used two 10ga. for the battery to fuse block to feed the 4.0mm and 12ga. for the two 2.5mm going to the relay panel in the engine bay. If you search well you can find my fuse block threads back in 2010 or so. I used 10ga. and 12 ga. , due to the short run from the battery to the fuse block. As your wire runs get longer, you will need to look closer at what ga you should use, maybe one or two steps larger.
Using GXL is a very good choice! Much better wire than GPT. Especially in the engine bay where there are high temps and moisture.
Good luck on your rewiring. Avoid short cuts in wiring and connections. Use quality crimpers and heat shrink where needed.
Tom

Something to note about the wire sizes listed in the German diagrams:
The sizes are NOT wire diameter, the units are "square millimeters".

So a 4.0mm squared is roughly equal to 2.5mm diameter.

Jim

Guys

Thanks for the responses. Based on the information, and Tom's terrific schematic he provided, I think I will use a waterproof Fuse Block with one input and four outputs (100 AMP Max with any single fuse not to exceed 30 AMPS). The plan is:

1. The Fuse Block input will probably be 4 AWG wire from + Battery post;
2. Each of the four outputs will be individually fused;
3. The two 12 AGW wires will have 20 AMP fuses (they will go to the relay board Pin 12 and Pin 14) and the two 10 AGW wires will have 25 AMP fuses (to the Ignition switch and Fuses 10, 11 and 12);
4. The wires will be sheathed with a thermal block as they route through the engine bay.

It maybe overkill, but I have had a few electrical mishaps over my 60+ years and with a full rotisserie build I want to minimize any potential problems. I may do something similar with extra relays for the H4 headlights. I will post pictures when built and installed.