After studying the wiring diagrams for the van (which, btw, can be referenced here: http://moparbvans.proboards106.com/index.cgi?board=factdiags&action=display&thread=241 )

I see that the feed from the alternator that charges the battery travels through the ammeter, feeding the fuse box and a couple other things before ending up at the battery. Since I upgraded my guages, the ammeter connections are bypassed and hooked together.

I'm in the process of figuring out how to hook up a battery isolator.
The one I chose is not a relay style, but a true isolator. One positive wire to each battery, and a hookup for the "field" from the alternator.

Since the alternator field line feeds so many things on it's path to the battery, would it not make sense to disconnect the black wire from the alternator and use it as the "feed" line from the isolator to the battery, and hook a separate wire from the alternator to the isolator field line?

Sorry if this is confusing, but honestly, so is the wiring in our vans, and I've been doing wiring in vehicles forever.

Anyway, in studying the wiring diagrams, I find that of the 3 wires out of the alternator, the 2 smaller ones (marked F1 & F2, which is confusing in itself when you're looking for the "field" line) feed the voltage regulator and ballast resistor, obviously not the hookups for charging. If under the current setup the black wire charges the battery, would it be safe to assume that I could change the terminal end on the black wire and hook it to the main battery terminal on the isolator, and then run a larger-gauge wire from the alternator to the terminal on the isolator that feeds both batteries?

I hooked up an isolator in a 75, 79, and 93, did all the same.

Cut the main charge line going to the battery, sent that line to the 'charge' or 'alt' post on the isolator, then the the other half of the already cut line went to 'Bat 1' on the isolator and ran a new wire from 'bat 2' to the new 2nd battery.

When I bought the one for the 93, there was a 4th post, I think that was for 'key on' power, had somthing to do with kicking on the isolator for charging purposes.

on the 75 and 79 I dont think I had to touch those 2 other field wires at the alternator at all.

Hope this helps.

Now that I see a wiring diagram! You don't really have to change the stock wiring, just add some cables.
The CatFish "Quick and Simple" plan:
1. Add a battery cable from the alternator output post to the "common" terminal on the isolator.
2. Add a battery cable from the "main" terminal of the isolator to the battery stud on the starter relay.
3. The "aux" terminal of the isolator will then connect to your second battery.
This will prevent cutting any stock wiring (which I hate to see happen), provide a high amp rated charging path from the alternator to the battery(s), relieve the firewall bulkhead connector from carrying the heavy charging load and will be simple to troubleshoot later if needed.
The only downside is the ammeter will no longer read correctly (since now the charging path is more direct) but a good voltmeter is better anyway.
PS. You would leave the black (A20) wire connected at the alternator. You're not removing or cutting any wiring this way.

you guys are awesome! Thanks so much!


And off I go.........more work to be done!

WOW, that was confusing. I have to look into this more next week, as I would like to have 2nd battery in for NATS.

OK, I'm embarrassed to ask this, but, if I simply add a second battery with an isolator, will that effectively give me twice the battery power if I don't connect any components (TV, stereo, lights, etc) specifically to it?

Meaning, will that automatically make it where all electrical runs off the second battery when the van is shut off?

If so, then, I think I could probably do that myself. If I have to actually wire things directly to it then it's gonna be way out of my league.

Thanks in advance for the education/flaming :-)

Whiff

U have to wire things to the 2nd battery.

There is a way add a second battery and double your battery power but I forget how to wire it, its either connect both positives together and both negatives, or negative to positive, I always forget. And no isolator would be needed.

adding another battery connected positive to positive, and negative to negative would double the amps that your battery has. Nothing would change about your charging system, except for how long it takes for the battery to run down when listening to the radio, etc, with the van off.

If your battery takes 3 hours to run down with the radio on, hooking a second battery hooked in parallel would double that time, but it would also take twice as long for the alternator to recharge the batteries.

If you're going to add a battery, and an isolator, I'd connect your tv, interior lights, etc to the second battery. That way, if you fall asleep watching tv, it wont drain the main battery, and the van will still start.

You can also find wiring diagrams on the last few pages of
the body builder manual i posted:

http://www.vannin.com/threads/ubbthreads.php?ubb=showflat&Number=203471#Post203471

It would apply to vans 77 and below.

Thanks everyone. Maybe I'll just pick up a genny or some other portable power. I'm not digging in to the harness, although CatFish's method is intriguing. :-)