Horn killing ignition? Am I crazy

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Hey folks, ran into either one heck of a coincidence or my horn is having an effect on getting 12V back to my ignition coil.

Car is a 1967 and has a few months old full wiring harness, not 52 year old wires.

I encountered an issue today where the engine cut out while driving fortunately in a parking lot walking distance from home.

Engine cranked fine, there was fuel to the carbs verified by seeing a squirt from the accelerator nozzles.

So, that left ignition. I walked home, got my multi-meter, a spare coil and a spare distributor.

Getting back to the car, the multimeter was picking up only about 1 volt from the wire from the fuse box.

So, I moved up to the fuse box and measure voltage there. When I touched the + lead of the multi-meter to the fuse, the horn sounded. I had a flash of embarrassment and pulled the lead off and it stopped, touched it again and it sounded. Pulled off and went back on and it didn't sound. So, I grounded the - lead and only got a 1 Volt reading.

Measuring straight off the ignition switch I got a 12V reading.

I went back to the fuse box and measured again and again, the horn sounded and this time did not go off when I removed the leads.

So I shut off the ignition which stopped the horn and then I removed the ground wire from the horn.

Turned the ignition back on and I had 12V at the fuse and 12V back at the coil and the car fired up.

Of note is the horn has not worked by pressing the horn button which I had believed was because it was wired wrong up there and I've just not gotten around to debugging that. Now is the time of course.

But, has anyone here encountered something like this where the horn will seemingly "steal" the voltage on that circuit?

[bluebus86]

https://www.thesamba.com/vw/archives/info/wiring/bug_67_USA.jpg

See above diagram. Two left most fuses are ganged together on positive input side, Bottom end of the fuse box on diagram. These two fuses are fed by ignition switch. now a short on the horn should cause the fuse to blow, and that not stop the car from running, as the wire to the spark coil is not on that side of that fuse, assuming everything wire wired correct per the diagram.

However, if the new harness had some of the wires swapped on the wrong side of the fuse, then the horn could draw down the coil voltage. id double check that each wire is on not only the correct fuse, but also on correct side of fuse, and that your sure the fuse box is not installed backwards.

Good Luck, Bug On, Beep, Beep!
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[Thread]

yup, checked that and it's wired correctly and I can't detect any shorts. I've got the Bentley manual and confirmed the wiring setup matches what's specified.

And to add more confusion, I've reattached the ground wire on the horn and I can't replicate the problem.

With the ignition on I get 12V to the coil on both sides of the fuse and I can't by testing the voltage as I was doing before get the horn to sound.

And, I pulled the horn button off to try and fire out what's up there and even grounding out the wire in the shaft I could not get the horn to sound.

Soooooooo. Hrm.

It's also worth noting that when I was not getting enough voltage to the coil, my gen and oil lights were nice and bright. The radio which comes off the ignition switch to a different fuse block was also operating just fine. Which I believe should rule out the switch being an issue.

I locked on to the horn because it was behaving oddly as described in the first post and the problem resolved when I removed the ground wire from it.

I'll be digging more into it tomorrow or this weekend. But, posting to see if anyone has experienced similar and can go uh huh yep, it's this.

If I'm the "first" I'll make sure to keep this updated with my findings in case someone else runs into it.

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Oh and worth noting, fuse was not blown and has solid continuity across its sides. That's true for both on that side of the block and well, all the fuses.

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Bluebus86 wins.

A casual glance like I did missed it. The coil wire was on the WRONG SIDE of the fuse and the horn wire was where the wire for the wiper should have been.

I also found that the person who did the re-wire wired the switched power for the VDO gauges to the pre-fuse side of the block off the ignition switch wire. Furthermore, that wire had a solder joint that looks like it could have been shorting out. Which is really strange because there's a separate fuse block specifically for the accessories like the gauges and the stereo system. So, I corrected that and replaced the wire and hooked it into the auxiliary fuse block.

I redid the wiring on the main fuse block according to the Bentley which should hopefully resolve the ignition issue from happening again.

On the plus side, the horn now works too.

I also found another oddity. The 4 way flashers didn't work properly (would just come on and not blink) after the re-wire and never worked before it. The oddity I found was a wire going from the second from the left (looking from the trunk) to the 54f terminal on the flasher relay. 54f is no where in the wiring diagram nor is there a wire going from that position in the fuse block to the relay.

So, I removed the wire and the turn signals still work and now the 4 ways work. Doing some research it looks like that terminal is used in the Type 2s.

So, all the wiring is now proper and hopefully the ignition issue won't reoccur.

[Thread]

I said I'd keep this updated with findings as I go and I think I've actually gotten to the bottom of it.

I noticed today that the windshield wipers were not working. Now, previously to this the coil wire was on the terminal that the wipers are now properly on (as well as the horn). This is an important bit.

Today I inspected and corrected every wire for the wipers from the motor, through the switch and to the fuse panel.

This didn't get them working.

Taking my multi-meter and doing a continuity test from the backside of the fuse panel from the terminal on one side of the fuse to the other didn't produce a tone on the meter.

Blown fuse I figured.

So I looked at the fuse and it LOOKED fine. Did a continuity test from one "end" to the other and I got a tone. Went back up to the backside and no tone. Went back to inside the car and I got a tone UNTIL i put the probes on the actual terminal ends where I got no tone.

I pulled the fuse and it still visually looked good but, on the ends there were what appeared to be some carbon circles or something on them. Touching the probes to anywhere outside the circles gave me continuity, anywhere inside no continuity.

I took some scotch bright to the fuse panel terminals and put a brand new fuse in.

The wipers started working no problem. I tossed the bum fuse.

So, the morals of the story appear to be:

1) Follow the wiring diagram for the car to the letter.
2) No matter what, don't put the ignition coil wire on the other side of a fuse from the ignition switch.
3) Don't trust a visual inspection of a fuse, always continuity test from one end to the other.
4) Patience in everything.

So, likely this fuse has been the problem all along. When the coil wire was where the wiper wire was it mostly worked until the fuse got to a position where no current was going across it.

But, good thing it happened (and in safe places) otherwise I'd likely never had looked at the wiring job closely enough to know it was wrong.

Also relevant, a new wiring harness works A LOT better than a 50 year old one. All lights and especially tail lights are much brighter than they ever were in my 26 years of ownership of this car.