Marc, Just for giggles, check the voltage of each of the red wires coming from the cabinet that were tied together going to the lp detector, should be different (house & chassis). Eric, the original detector had 2 energy sources. That was eventually superseded by the house battery only. The picture proves my point of an ignorant installation tying both energy sources together.
Marc, is the dash switch momentary, on-off, or on-off-momentary and how is it identified? Here is how the echo charger is engineered: It gets its power from the HOUSE battery thru the yellow 15 amp fuse (solid red 14ga wire). When it senses 13.1 volts it then knows the house batteries are being charged (solar, shore power, ect) It then trickle charges the CHASSIS batteries thru the yellow 15 amp fuse (red wire with yellow stripe) This will never take the place of a 200 amp solenoid. The green LED will indicate operation.
All solar panels must have a controller to regulate output (no controller equals fried batteries) Mppt controllers do the best job but are more expensive.
Perhaps someone out there in Forum land could chime in that owns a 98 Ticonderoga and send some pictures of the original configuration on the engine side of the bed pedestal.