Re: 90A Battery Isolator
So far I have not been able to get the picture to post but the instruction are below.
The bottom line is you probably do not have to do anything as it is probably already wired the right way. When you wire your isolator the output wire from the altenator, the large usually red wire that usually goes to the post the main battery connects to which is useally on the starter or starter solenoid. This large wire usually 10 guage red will need to be cut. The side from the alternator goes to your isolator common post. The side that goes to the battery will go to isolator output 1.
Your second battery goes to isolator output 2.
The second and 3rd wire to the alternator normally do not have to change at all.
One will go to the ingition switch and is the smaller of the two wires. The other is larger about 14 guage usually red or orange is the sense line and it goes as near to the battery as possible. It will normally go to the same post on the starter as the other.
The only time you would loose the .7 volts is if it was connected to the common post on the isolator or the alternator output. As long as the voltage sense line is connect on the battery side of the isolator you will not loose the .7 volts.
This is only true with a 3 wire alternator. It is different with a 1 wire alternator or an outboard. I do not know why people constantly say you will loose .7 volts to the battery.
Do It Yourself Hot Rod Kustom Website
Electrical - Wiring up the Alternator
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Electrical - Wiring up the Alternator
1976 Camaro three wire alternator
One of best inventions in the early 70s, is the three wire alternator. The voltage regulator is built into the alternator. This makes it very easy to wire up and it also has the added benefit that the voltage regulator is no longer a mechanical device but now semiconductor based - no adjustments!
There is a common misconception about alternators and the term one wire alternator is often thrown about. Most people mistakenly identify a 3 wire alternator as a one wire alternator (I know, I was one of those). A one wire alternator was only used for limited applications and has distinct disadvantages. The 3 wire alternator is a proven design and has been used for the past 30 years starting in the late 60s, early 70s. Here's a website that discusses the advantages of a 3 wire alternator over a one wire: Advantages of a 3 wire alternator
3 wires are actually used plus chassis ground
There are 3 wires needed to run it and the case provides the path to chassis ground Even though there are 3 wires, it is very easy to wire up. Here's a desciption of the wires:
Battery positive (Bat+)
connect to starter +12V battery wire
use 10 ga wire (thick)
Screw on terminal on the back of the alternator
Voltage sensing line
connect to the Bat+ close to the firewall
Senses and adjusts the +12V were it is needed
use 14 ga wire (thinner)
Pin 1 of the push in connector on the alternator
Ignition On input
When the ignition switch is turned on, power from the ignition switch turns on the alternator
Pin 2 of the push in connector on the alternator
use 18 ga wire
In the above pictures, you can see a black wire that is connected to the alternator mounting bracket. I ran an extra ground wire from the firewall directly to the alternator's mounting bracket just cause I'm paranoid about bad grounds. Normally the engine has a ground strap between it and the firewall which provides an excellent ground. I've painted all my parts and want to make it 100 percent sure. Most likely it is not needed as millions of cars work perfectly fine without it.
Between the starter and the battery is a short piece of wire about 1" long that is a smaller gauge than the main wire. It is a fusible link. The idea is that if there is a catastrophic short in the wiring harness, the fusible link will burn up before the rest of the wiring harness. It operates on the same principle as a fuse.
