Wait -- never mind. An archives search turned up a nice description by
Mark Drillock of how to use the Westy kitchen fuse block to get the
relay drive from.

Mike "Rocket J Squirrel" Elliott
71 VW Type 2 / 84 Westy: A poor but proud race.
KG6RCR

Rocket J Squirrel wrote:

> Is there a schematic of how Sean probably has his aux battery setup
> wired?
>
> I've also heard there is a nifty way to connect the relay to the
> alternator idiot lamp so the relay kicks in when the lamp dims. But it's
> not clear to me how to do this -- doesn't the lamp light when the
> battery voltage is lower than the alternator output? Where would the
> relay be connected in this case?
>
> After discharging the main battery on my last camping trip I've ordered
> an Optima and the hefty Stancor relay.
> --
>
> Mike "Rocket J Squirrel" Elliott
> 71 VW Type 2 / 84 Westy: A poor but proud race.
> KG6RCR
>
>
>
> mark drillock wrote:
>
>> If you read your link, Sean used a RELAY instead of an isolator with his
>> Optima dual battery setup. He also added an inverter. He first tried the
>> wimpy relay kit sold by TBD but switched to a REAL relay that costs
>> about $20 and can handle 100 amps.
>>
>> http://www.vgonman.com/auxbat.htm
>>
>> Mark
>>
>> randy charrette wrote:
>>
>>> I'm no electronics expert, so I found a web site (www.vgonman.com)
>>> and copied his set-up. It has worked great for about 3 years now.
>>> This is set-up with a isolater.
>>> Randy
>>> 87'Syncro TIICO
>>>
>>> David Marshall <VANAGON@VOLKSWAGEN.ORG> wrote:
>>>
>>> I can't see an issue with a 70A relay load wise as your alternator is
>>> 90A
>>> and only on a good day. I use a generic Bosch 40A relay for my 2nd
>>> battery
>>> in my TriStar and I have never had an issue and I have a 120A
>>> alternator.
>>> Charging battery from a dead flat doesn't make the relay nor the
>>> 2x12ga wire
>>> running to the battery hot or even warm to the touch. I think the
>>> relay is
>>> the simplest and probably the most effective of designs. The diode
>>> isolators are not good in my opinion as they introduce a 0.7V loss in
>>> the
>>> system over both batteries. The computerized isolators that give the
>>> starting battery and deep cycle the voltage they want to see is the
>>> best
>>> bet, but expensive and really I think the deep cycle will charge fine
>>> on the
>>> relay with an alternator designed to charge a starting battery.
>>> 1000s of
>>> fishermen driving home charging their deep cycles on their F150
>>> can't be
>>> that wrong.
>>>
>>>
>>
>