I have a script set up for my mod that I'm working on, Fighting Fatigue. One of the features is reduced speed when wearing one or more piece of heavy armor. I have a Detrimental, Hide in UI, No Area MGEF which is a value modifier, constant effect, for SpeedMult.

I then have the MGEF on my spell, with conditions. The conditions are so:

http://i1295.photobucket.com/albums/b630/Matthiaswagg/Screenshot26_zps49166ebb.png

This is the MCM script that allows you to set the magnitude of the MGEF, and toggle it on and off.

http://pastebin.com/VSFYMBVn

The issue is that, once it's been toggled on, it seems to stay, even if you toggle off the value. Changing the magnitude of the spell via the MCM seems to do absolutely nothing.

Could anyone provide some input on this?

EDIT: And now, I'm wearing iron boots and an iron cuirass with other light armor, and I'm literally shooting across Dragonsreach I'm going so fast. I think I might just remove this feature...

IIRC There is an issue with SpeedMult which requires you to add and remove a token item of weight to the characters inventory before it works properly.

I do so. If IIRC it didn't even need to have weight, but just be an item. I do so with an ObjectReference called Weight Item in the script I linked. I'll try giving it a miniscule weight instead of no weight.

I'm just not going to use it since it just seems to ruin your speed. When you toggle it off you just get faster and faster until you're like the speed of light or something.

There's not really enough info here to determine the problem. But it is possible to create successful speed mult modifier abilities.

This is the script I have used many times and it has never failed me, simply attach this to your speed mult magic effect. It ensures the effect takes place immediately and also that speed is restored to normal immediately after the effect ends.

Scriptname EA_SpeedMultMGEFActivator extends ActiveMagicEffect;This script applies an invisible carryweight modifier;to the target of the magic effect, which will force;the game to register any Speed Multiplier changes.Event onEffectStart(Actor akTarget, Actor akCaster)	akTarget.modActorValue("CarryWeight", 0.01)EndEventEvent onEffectFinish(Actor akTarget, Actor akCaster)	akTarget.modActorValue("CarryWeight", -0.01)EndEvent 

That said, it sounds like something else might be going on with your problem anyway, so not sure if this would solve the problem. You should do some debugging with the Trace function and your papyrus log to help see where things might be going wrong in your script.