If you’re fixing an old train or some other electrical device, some of the wires have crumbling insulation, and disassembly isn’t an option for whatever reason, then you can repair crumbling insulation with a $6 product called Plasti-Dip.
What you need
Surprisingly, for this project you only need two things:
First you have to decide if you want to shore up the existing insulation or replace it altogether. If the insulation is crumbles when you touch it, your best bet is probably to crumble off as much of it as you can and replace it. If the insulation that remains is in good shape, and stands up to routine handling leave it intact and fill in the gaps instead.
Repair crumbling insulation
Position what remains of the crumbling or broken insulation to eliminate as many gaps as you possibly can. Use a drop of cheap super glue to tack each piece of insulation into place.
Next, brush some Plasti-Dip into the gaps to cover any and all bare wire. Try to apply enough to bring it as close to the thickness of the remaining insulation as you can.
Finally, brush a nice, thin layer of the Plasti-Dip on top of the remaining insulation. This will shore up that remaining insulation and help to stick all of the new insulation together.
Let it all dry. Once it’s dry, you can reassemble your electrical device and let it get on with its new life.
If disassembly is an option, there are some other things you can do to repair insulation.