==Design Error + Missing Fuse = Ignition Conductor==

MNAirHead · Post by **MNAirHead** » Tue Jun 09, 2009 2:26 am

I'd like to start a banter on probably the biggest classic VW blunder that never got fixed.

Fuse the wire between your ignition and your coil/choke... if this dead shorts, the wire going through the loom will glow red hot and melt your harness.

There's a design problem that gets even worse if you run a Webber progressive - the choke wire is about 3 mm from the fan shroud...

How do you prevent this melt down? (being "careful" is more like "lucky" in this instance)

Post by **Piledriver** » Tue Jun 09, 2009 3:15 am

The simplest fix is put a fuse in the line up front, but that is not the best fix by a longshot.

Run fused 12v (off the starter/direct from battery or alt) to a relay in the engine compartment and power the ignition etc. off that.

(The original wire should ONLY control the relay, and the fuse box end can still be fused with a small fuse)

Note this also actually provides full battery voltage to your ignition/choke/backup lights etc circuit... This is a major feature, the old run was long, and the wire is small and old.

Also, if you do somehow manage to cook this "new" power feed wire, it doesn't melt into and take out the rest of the rear wiring harness around it.

Just use a waterproof inline fuse holder (spade type best) next to the relay screwed to the firewall or fan housing. Use fully insulated terminals.

The only other design flaws more likely to burn down your car are the steel fuel line running through the front tin (Needs a proper feedthrough) and the press in gas fitting in the Solex carbs. (Needs tapped and a barbed fitting installed)

OT, I highly recommend doing the same "add a relay" trick for the headlights for safety reasons, although the "safety" improvement is mostly better visibility. (This skips the ig. swicth and the light switch in the power feed, and they will likely be MUCH brighter)

MNAirHead · Post by **MNAirHead** » Tue Jun 09, 2009 4:15 am

PS.. Piles method also doubles as a theft deterrant.

Post by **2088 bob** » Tue Jun 09, 2009 5:18 pm

I think Piledriver pretty much nailed that one. I would install the inline fuse as far forward in the cct as possible

MNAirHead · Post by **MNAirHead** » Wed Jun 10, 2009 3:10 am

Bob.. I'm guessing that you're not a fan of the 69 cent auto store fuse.. is there a specific method you'd suggest? Meaning is there a hidden gem with few connectors etc.

Please nobody ask how I know this wire can go up in flames...

Post by **2088 bob** » Wed Jun 10, 2009 9:49 am

just use one of those oem style vw fuse holders ,like the ones i have seen that go to the feed for the backup lights, should do just a dandy job a couple of .250 appliance sta cons and you are in business

this is what we refer to as a appliance sta-con

http://www.elecdirect.com/product/65fe7 ... 8f586.aspx

Post by **david58** » Fri Jul 03, 2009 12:01 pm

Any reason why the power to the coil couldn't be just moved from the hot side of the fuse panel to the fused side of the fuse panel?

sideshow · Post by **sideshow** » Fri Jul 03, 2009 1:05 pm

david58 wrote:Any reason why the power to the coil couldn't be just moved from the hot side of the fuse panel to the fused side of the fuse panel?

Because it doesn't use the panel.

Post by **david58** » Fri Jul 03, 2009 1:36 pm

sideshow wrote:
david58 wrote:Any reason why the power to the coil couldn't be just moved from the hot side of the fuse panel to the fused side of the fuse panel?
Because it doesn't use the panel.

I think it does on my 74 bug I will take a test lamp to the house to verify and post up results. If this is true then I can move the wire to the fused side of the panel. Only question is will it draw too much amperage? The lower part of the panel is hot with the key on the fused part of the panel is the upper part power has to go thru the fuse for it to be fused.

Post by **david58** » Fri Jul 03, 2009 2:56 pm

So there are two ways this could be done.
1. Just add a inline fuse between the fuse panel terminal and the coil power supply wire.
2. Move the coil power supply wire to the terminal above the fuse.
Now which is the best choice and what amperage fuse would it take?
There is a spare spade connector above the fuse. The only thing hooked to it is power to the speedo cluster.
Just moving the wire above the fuse is the easiest thing to do. You don't have to add or buy anything.

Post by **Piledriver** » Fri Jul 03, 2009 3:10 pm

No, you don't HAVE to add or buy anything.

I just find actually getting 12V to the coil works better than 9ish...

There's a lot of old wire/old connections and an old ignition switch in that circuit.

IMHO, best use for it is to just operate a $5 relay.

Post by **david58** » Fri Jul 03, 2009 3:16 pm

Piledriver wrote:No, you don't HAVE to add or buy anything.

I just find actually getting 12V to the coil works better than 9ish...

There's a lot of old wire/old connections and an old ignition switch in that circuit.

IMHO, best use for it is to just operate a $5 relay.

EDIT Ok I jumped in here on the end of the thread. I had read the whole thread previously and kinda forgot about the relay. What we need to add to this thread is how to diagram to wire the relay. I was trying to show how to fuse the circuit as close to the power source as possible. I don't think it is a bad idea to fuse the coil wire at the fuse panel for added protection since it runs thru the car.

Post by **Piledriver** » Fri Jul 03, 2009 9:09 pm

It's not a bad ideal at ALL, and folks should probably all run out and do it yesterday... but long term, the relay works better, and the fuse should still stay.

Any unfused wire is an accident waiting to happen.

sideshow · Post by **sideshow** » Fri Jul 03, 2009 9:37 pm

I like the stock, no fuse, only one wire back to the coil design.

The bad name was probably more due to expert designs like wobbly weber progressive manifolds (or choke less, or dual chokes, funny how people can't figure out small stuff, back light switch) and other after thoughts.

The only issues I have observed have directly involved added on wiring. Keep that circuit simple and it is a non issue.

Post by **david58** » Sat Jul 04, 2009 5:40 am

Piledriver wrote:It's not a bad ideal at ALL, and folks should probably all run out and do it yesterday... but long term, the relay works better, and the fuse should still stay.

Any unfused wire is an accident waiting to happen.

I totally agree that the relay needs to be added the old coil power supply wire it is a weak point in the ignition system. It could be the actual cause for a lot of gremlins.

Edited for Clarity wrote:Just like Pile said he would rather know he has minimum 12 volts to the coil than have maximums 9ish volts there.

It is kinda hard to tell 9 volts from 12 volts with a test light.
If you check the battery voltage ( engine off) then check the charging system voltage ( engine running at 2500 rpm's) then do the same tests on the coil wire at the coil you can see if you have a voltage drop at the coil. But don't stop there put a load on the system turn on the high beams crank the engine over and see how many volts you have going to the coil now while cranking.