Can anyone explain why I keep overloading?

[sweetidealism]

Most attachments work without its corresponding maneuver, and you're right the more maneuvers of the same element that are active the more powerful the attachments get. Such as the tension spring, with no fire maneuvers you get 3% more attack, with every subsequent fire maneuver active you get an additional 3% attack.

Other attachments require or consume maneuvers for them to work, they are (I might be missing one or two):
Fire Attachments
Flame Holder
Heat Capacitor
Reactive Shield
Strobe

Ice Attachments
Ice Maker

Wind Attachments
Barrage Turbine
Replicator

Earth Attachments
Hammermill
Schurzen
Shock Absorber

Thunder Attachments
Volt Gun

Water Attachments
Condenser

Light Attachments
Auto-Repair Kit/Auto-Repair Kit II*
Eraser
Flashbulb

Dark Attachments
Disruptor
Economizer
Mana Converter
Mana Tank/Mana Tank II*

*The repair kits and mana tanks will increase your puppets max HP/MP without maneuvers by using their respective maneuvers you get a regen/refresh effect.

Incidentally, Volt Gun does work without active thunder maneuvers, but it's proc rate will be fairly low and it won't be as potent when it does proc.

[Telford]

Incidentally, Volt Gun does work without active thunder maneuvers, but it's proc rate will be fairly low and it won't be as potent when it does proc.

Egads you're right! Not having used the attachment since I started playing pup I assumed it worked like the reactive shield. After actually looking at all the attachment pages I found a few I missed so updated my post, thanks sweetidealism.