Alternator backfeed to coil

[CruisinGA]

I'm about halfway through installing a 12SI Delco Alt into my '74 40.

One of the terminals on the alternator needs a switched 12v source. You cannot use the ignition coil supply (unfortunatly) because the alternator will backfeed through it.

What I am specifically wondering is if I can use the ignition wire that used to connect to the voltage regulator, without having to install a diode into it. I already have the PS wiring loom apart to pull out all the unused wires, so it would be easy to run.

 

[Mark W]

Use the acessory circuit.


Mark...

 

[jeffery_1965]

In this thread: https://forum.ih8mud.com/showthread.php?t=115210 I described how I handled the excite wiring. See the last post.

The short of it was that I used the switched wire that went to the old voltage regulator ('77 fj40). I tried it without the diode and it worked fine, but I did install the diode anyways.

Hope that helps,

Jeff

 

[grant5127]

https://forum.ih8mud.com/showthread.php?t=116504 post #28

 

[Gumby]

relay


the accessory circuit is easy too

 

[Eric_FJ40]

I put in an "idiot light" in the dash rather than a diode. I picked up my switched power at the fuseblock - ran to light in dash - and out to the alt.

Works great for me.

 

[Pin_Head]

I would prefer the old voltage regulator wire that is a part of the "engine" fuse circuit. If you use the accessory wire and leave the key in the Acc position to listen to your radio, you will have a 5A drain energizing your alternator for no good reason.

 

[CruisinGA]

Hadn't thought of the acc circuit..

Thought of using a relay, but that seems to add complication vs a diode

It just seems "right" to use the old voltage reg wire, so I picked up a diode today to install into it just in case.

Finishing it up this afternoon...

BTW- thanks for the wiring description in the other thread, Pin head, that's mainly what I am going by.

 

[Gumby]

I picked up a bank of relays off of some car. They all seem to have them these days. One runs my cooling fan on low, one on high, one powers the alternator, one will switch the air, etc.

The alternator relay is easy. Two wires to power, one to ground and one to the alternator. When the power is turned off, the relay breaks contact and the power is shut off to the alternator.

Another issue was the 120A alternator that came with the serp belt system was a bit much for the stock wiring. It let all the magic smoke out of the wire the first time it tried to recharge the battery after starting. A 10ga. wire from the alt to the battery solved that, but my amp gauge no longer is accurate. Not that I wanted 120A running through my dash anyway.

 

[CruisinGA]

Gumbo- I know how to wire a relay Its just 3 less wires and 6 less connections to fail when I don't use one.

The way I've got this thing set up now, the stock ammeter still reads the same information as the old one, but the alternator charges the battery through a 6 ga cable directly to the battery.

Only thing I'm suprised at is that the alternator is putting out 14.5+ volts all the time. Seems high compared to what the toyota alternator ran.

 

[Pin_Head]

The way I've got this thing set up now, the stock ammeter still reads the same information as the old one, but the alternator charges the battery through a 6 ga cable directly to the battery.

.

If that amp meter mod worked out, you need to write it up and post it. It's pretty cool

 

[CruisinGA]

I am going to do a writeup on the whole deal- even took a few pictures along the way.

 

[handcannon]

I am going to do a writeup on the whole deal- even took a few pictures along the way.

I am very interested in what mods you did to make your amp guage read the same as stock. Between working overtime, working on the house, and the holidays I am behind on my switch to a higher amp alt. But, it's coming real soon and your info would be handy to have at that time.