120 amp alt--B+ to Batt or Junction Box?
 

I've read of some people wiring the B+ of their new alternator
straight to the battery and others wire it to the junction box.
Does it make any difference if you do it one way or the other?


Jeff

it depends on the wire size from the junction box to the battery...

On my '84 Euro TD, I wired the alternator B+ to the battery terminal at the starter.
I used a light-duty WalMart battery cable, with a stamped battery terminal and an 8mm lug that bolted right onto the starter terminal. I then cut off the ring-part of the stamped battery terminal, leaving one 6mm lug that bolted perfectly onto the B+ alternator terminal. After enlarging the hole from 6mm to 8mm in the leftover ring-part of the battery terminal, I wrapped it around a bit of rubber fuel-hose, to support the mid-point of the battery cable at the intake manifold brace where it fastens to the stud under the manifold.
However, unlike an SD, my Euro TD has no turbo plumbing in the way.

Happy Motoring, Mark

In our 420SEL when I wired the alternator to the distribution block on the firewall I found that there was 0.5 V drop between that point and the battery terminal.

I decided to run the wire directly to the battery rather than gut the distribution block and upgrade its wire to the battery.

I would recommend doing the same for any new installations. My 300D's 150A alternator goes right into the battery as well. My 190E does not simply because I haven't fixed it yet. I used a different cable that is less flexible. It was the first upgrade I did.

Thanks for the input. In looking at the wiring to and from the junction
box, it's quite a rat's nest. Didn't know if the power had to pass through
something between Battery & alt for some reason.

Attached is photo of junction box for vstech.
two red wires come from the old three prong alt plug.

I was going to put in a single new 2 ga copper wire straight from
alt to Battery + and cut and reattach existing blue wire.

Jeff

I know well what's stock on the 123/126 wiring... my point is, if you run to the junction block, you need to also run to the battery FROM the junction block or you are not accomplishing anything.
upgrading only the feed to the block will just move the point excessive current smokes the wire.
and know this:
putting on a 120 amp alternator will not overload the wiring unless your battery runs down, or you add additional components to the car.
it just lightens the load on the alternator.

Here are some photos from the install on our 420SEL:

http://imgur.com/a/wP7GX