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MG MGA - Another alternator mod question

The Moss instructions for alternator wiring states:

"There should be two wires at the A terminal [of the voltage regulator]. Of these two wires select the one that does not go to the battery and attach the yellow wire tap provided."

Here is my conundrum for you guys with electrical engineering degrees or more just common sense than I possess:

Both wires are brown. Both disappear into the wiring loom just a few inches from the regulator. One wire goes to the battery, one goes to the fuse block. Both are soldered to the female spade connector that attaches to the voltage regulator. Because they disappear into the loom and they are both brown and the same gauge wire, it is impossible to tell which is the battery wire and which is the fuse wire. I could snip the wires at the spade connector and test conductivity...or take the lazy way out and turn on the battery switch to see which is live...but here is my question: if I do not cut the wires, does it really matter which one I tap, since both wires are securely soldered to the same spade connector?

Or is there an easier way to determine which is the battery wire?
Frank Nocera

For the archives: I disconnected the wires at the spade connector, found the hot wire, tapped into the other brown wire (the one going to the fuse block) and then resoldered the wires together onto a new female spade connector. Job done, alternator light working properly, alternator charging nicely.
Frank Nocera

Frank,
You could have also checked continuity from the female spade to the end of each brown wire by disconnecting both of the component ends (fuse block, etc). As long as both of the far ends were disconnected at the time you checked for continuity from the female spade connector, each would have been isolated from the other and any other part of the electrical system. Sounds like something you might want to point out to Moss for future clarity in their instructions. I know I valued such feedback from those who used my Bosch conversion site.
Bob Muenchausen

Hmmmm. Bob, I'm missing something. Probably me being dense. The two brown wires were twisted together and soldered to the one female spade connecetor. If I had disconnected the opposite ends of the wires at the fuse box and starter switch, and had applied power at the common spade connector, BOTH would still have given a continuity reading at the other end, right? So if both were showing conductivity, wouldn't I still be in the same quandry of not knowing which one went where when it disappeared into the wiring loom behind the hearter box, a few inches from the regulator? More importantly, since both ARE soldered together at the spade, which only serves now as a terminal block, does it really matter to which one the alternator yellow wire is tapped into? If so, why?
Frank Nocera

No, Frank, because your continuity tester would have only tested between the "common" female spade and the one other end you connected its other lead to.

That is, if you disconnected the end at the starter switch AND the one at the fuse box, and then measured from each of those ends to the "common" soldered female connector, the only complete pathway for electrons for your continuity tester/meter would be via whichever section of wire you connected its leads to, ie: from the connector on the starter switch lead to the common female OR from the fuse box lead to the common female.

You would ONLY have continuity on both sections at the same time IF you connected the leads from your continuity tester/meter from the starter switch connection to the fusebox connector. Then you would have a complete pathway through the whole of both wires by virtue of their having been joined by the female spade connection.
Bob Muenchausen

OK, Bob, I understand the continuity issue now.

But getting to my other question, does it really matter to which wire the splice from the alternator is made? If so, why? (And won't the splice risk letting the smoke out of the Lucas electrical system?)
Frank Nocera

Frank,

No it doesn't matter! I hope you turned the smoke supply off before making the splice.

Bob,

While you are correct in the continuity issue, Frank wanted to identify which wire at the regulator connected to the fuse box - the ONLY way to do this with a tester is to separate the wires at the regulator!
Chris at Octarine Services

Good point Chris. I was seeing the wiring Frank was talking about in my head as separate from the harness, and that is simply not reality. Thanks for the correction, I am sure it served Frank better than my comments.
Bob Muenchausen

This thread was discussed between 29/01/2005 and 06/02/2005

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This thread is from the archive. The Live MG MGA BBS is active now.