I have a 1968 Beetle and am wiring up a tacho. Many years ago I threaded electric cable through the big grommet behind the voltage regulator under the back seat through to the engine bay however now I want to upgrade that cable, I am struggling to pull the new cable through. Any suggestions?
Cheers

Take it through the roof (up the front pillar and down the back) This is how i did my 66 get some yellow tongue ( plastic strap) to go the required route,
tape the wires to the end and then pull the guide through
easy???

Not easy

On the later Superbugs the loom runs over the rear wheel arch behind the back trim panel, then through the "C" pillar gap (where the foam lives) and into the engine bay on the top LH side.
From inside the wheel arch you could run it under the back seat, or clip it to the heater channel to floorpan join and run it up to the dash/bonnet area that way. Neat and tidy with no drilling.
I would suggest running trailer cable for the job. It's thick enough to push through OK, carries 5 or 7 wires in case you decide to upgrade to a bank of gauges or a fancy ignition system later, and each wire is rated at 10A.
Oh yeah, and it's cheap!
Loop up the excess in the top LH corner engine bay and you won't even know it's there.

I made the mistake of having my headlining fitted before I had run the extra cables.
I did as above, went to an electrial supply shop and bought whats called a snake, its thin plastic strip about 5 metres long and about 3 cm wide
I drilled a hole in the end and tied a piece of sting to it and fed it from the rear, i had removed my interior light and managed to find the end there.
I then pulled the string out through the interior light hole and then did the same from the front to the interior light.
Tied the two strings together then I used that to pull some 5 core wire through.
Took 20 mins.

Do you know a sparky with a snake reel? It's what I know it as but basically a narrow coiled wire that can be passed down things and can flex around corners.

With this you should be able to feed it up the front windscreen pillar and then making it's way to the back will be pretty easy. Going the other way may prove more tricky due to the tight bend of the windscreen and the length of snake already used. Some can even be driven by a motor so the spinning action helps the snake bend around things

Thanks everyone for their suggestions. I wanted to replace the cable that I had installed years ago along the floor cable tied to the main loom, rather than running one through the roof (which I must admit I hadn't thought of.
Modnrod reminded me that on my model you need to remove the rear side trim card. Once I did that it was easy as. I even fed the cable through encased in some split tubing. And yes '68's have foam too.
When the headlining is replaced I may well run some cable through the roof as well for any future upgrades
Cheers

Hmmm. I'm interested in your comment about the foam in the 68.

I have a 68 which I am restoring and has been in the family since new and definitely no foam. What iis inserted is this wedge-like pad made out of original headlining material which is stuffed with some sort of cotton waste or something and then inserted into the gap. This pad can be removed from and replaced back into the C pillar in one piece.

Anyone else got this or has got foam?

viiking

Some had the pillows in them and they don't have the same problems as the foam filled cars so you are lucky. Keep the pillows if you take them out as you can put them back in and it stops vibrations from happening.

Yogie

Yep, those triangular pads are there to stop engine noise travelling up the roof channels and into the cabin plus any possible engine fumes.