Yep, if triggered only when the engine is running then the draw of the
solenoid coil is of no major concern. Some people try to use a selector
switch to let either the alternator blue wire control it or select
battery voltage to force it to combine during engine off charging,
whether by trickle charger or solar. In both cases the draw of the
solenoid can waste much of the charging current. Also some dual battery
automatic combiner products use solenoid relays and those need to be
chosen carefully if solar or trickle charging is planned.

If using the blue wire to control it on a Westy and the 3 way Dometic is
still present I would consider use of the output of the fridge relay to
also drive the solenoid coil and reduce the load on the alternator blue
wire.

Mark

Don Hundt wrote:
> If the solenoid is triggered by the blue alternator wire, it would only be
> activated while the engine is on. If you install the solar panel wiring
> downstream from the solenoid it shouldn't affect it .
> Don
>