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Alternator wiring question

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bash

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After a dead battery problem last week, I finally decided to change my Lucas 18ACR (possibly original 1975 vintage) for a new/rebuilt Bosch. I figured the extra 10 Amps would be useful since I have added an electric fan, a stereo and various other extra demands. I stopped by an Alternator shop today and they didn't have one on the shelf, so they built one for me, and they very kindly used parts to make it a 72A max output, instead of 55A. Whether they were being kind or only had those parts available I don't know.

I am the first to admit that I don't really understand electricity, but the prospect of putting out a very large current, say if my battery is a little discharged, is rather worrying to me, so I wondered if it would help to add a new 8 or 10 gauge wire from the B+ terminal to the starter? I will reuse the original 3-pin plug, so this would be in parallel with the original wire, I think. Is that how it works?

Also, does anyone know the length of the original fan belt for a '75 TR6? My alternator sits closer than I would like to the engine, and makes installing the fan belt really difficult!

Thanks in advance for any advice
Alistair
 
Just measure your existing belt and take it to NAPA and get one 2-3" longer.

If you run a 4 or 6 gauge wire from the starter connector, back up to the alternator in the place of the heavy brown wire used in the stock harness, you will never have a problem with the alternator wiring again.
 
Adding a wire certainly won't hurt, but the original brown wire was big enough IMO. Any problems usually arise at the connectors.

I would just take your old belt with you to NAPA. Hand it to them and say "I need one an inch longer than this" (Or two inches, if you are sure you want that much.)
 
not sure about your 75 model, In dan masters book, for an amp gauge if you want the amp gauge to work as intended, you could run a paralled brown wire to the amp gauge and then to the starter, and also add a shunt from one post to the other post on the gauge. the shunt will split the load thru the amp meter so the needle doesnt peg either way. Now with the volt meter I dont know what you do but you could just run your heavy gauge wire from the alternator directly to the positive post on the battery. Same as going to the starter just a shorter route

Hondo
 
Thanks for the advice - if Randall thinks the original wire is okay, then that will do for me! It actually looks pretty thick, though it could be realy thick insulation for all I know.

I had another go at making the old fan belt fit last night, and noticed that the size is stamped on it - 12.5x1125, so I guess 1/2 inch by 44 inch (well 44.5 inch, really). I figured it would be helpful to have the new belt in hand when taking the old one out, to avoid messing around jacking the engine up twice. I switched to the early mounting bracket (and engine front plate) a few years ago and never switched the fan belt to suit - the only way to change the fan belt at the moment is to remove the alternator mounting bolt, which makes it even more of a pain. Hopefully a 46 inch long belt will give me an inch or so of extra movement.

Thanks again. I know it's been said before, but the Bosch alternator really does just drop straight in!
Cheers
Alistair
 
The only reason for the new, heavier wire (and I basically agree with Randall) is that in the event your battery goes dead and you send a full amperage charge to a dead battery on a weak old wire, you could burn it up. The old 34 amp is a lot less than the new 72 amp.
 
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