Either way works for the blue wire relay trigger hookup with 2 small
relays. I prefer to let the blue wire control just the stock relay and
then use the output of that relay to trigger the second one because I
often use larger sizes of second relay. The stock fridge and aux battery
relays are a small type that draw very little current from the blue
trigger wire but bigger relays draw a lot more from it than was intended.

The main aux battery issue is where the charging power for the aux
battery will come from. Using the existing 12 volt power wire to the
fridge relay to also charge an aux battery just does not work well. It
can work to keep a charge on it until you camp for a while but once you
drain the aux battery that shared power wire won't charge it back up in
a reasonable time, particularly if the fridge is also running and/or the
headlights are on. You need a separate power wire from the main battery
to the aux battery relay to re-charge a drained aux battery consistently.

Mark

miguel pacheco wrote:
> That bit about the factory relay being wired to the fuse panel makes
> sense to me Mark. So this second relay would get it's signal from
> terminal 87 on the factory relay? Or could the blue wire energize two
> relays or is it too weak?
> Miguel
>
> I have not failed. I've just found 10,000 ways that won't work.
>    - Thomas A. Edison
>
>
>