TheSamba.com :: View topic - Hot wiring and I apply +12v battery to + on coil the horn beeps?

Fri Jul 31, 2020 10:56 pm

Been working on my 1974 original engine, original dual solex carbs. I don't always have a helper to sit in the front and crank the engine while I work on stuff to get it set up. Meanwhile, I've cranked it over with the ignition key plenty of times and everything is going as I would expect (except not running nice yet and hard starting).

So I build a simple hotwire box so I can do it all from behind the bus. It hooks up to the battery positive and negative terminals. It has two simple switches. A toggle switch to provide 12v to the coil and a heavy-duty momentary push button switch to provide 12v to the spade terminal on the starter solenoid. The LEDs simply let me know my toggle and pushbutton are putting out 12v as expected. I have a fuse in the main +12v wire from the battery to the hotwire box.

However, when I turned on the toggle switch to provide +12v to the coil, my horn activates. What super-simple concept is eluding me? Yes, the push button for the starter solenoid works fine and the engine turns over. Yes, the toggle switch is providing 12v to the coil.

Weird and very unexpected. The horn was not activating when starting from the drivers seat with the key.

Sat Aug 01, 2020 3:35 am

That’s quite a list of cars you have in your signature line. Could your hotwiring skills have anything to do with that?

Sat Aug 01, 2020 3:38 am

I’m guessing your horn wiring is not stock

Sat Aug 01, 2020 6:14 am

aeromech wrote: That’s quite a list of cars you have in your signature line. Could your hotwiring skills have anything to do with that?

Apparently not. I'm guessing that guys who hotwire VW buses in the middle of the night to steal them don't want the horn going off instead of the engine starting.

Sat Aug 01, 2020 6:32 am

A couple other things to mention.

1. There are two spade terminals coming off the starter solenoid which I believe one is from the ignition on the steering wheel for starting and one goes to the positive terminal on the coil to supply +12 while cranking. In order to "hotwire" the starter solenoid with another source of +12 to that dual spade connector, one of those wires has to be removed to gain access to a connector. I chose to remove the wire coming from the ignition and hooked my momentary switch wire to that spade terminal.

2. The wire coming from the ignition switch that I removed was a PO-installed heavy wire going to the front of the bus and one of those typical relay circuits to provide more power/current to the solenoid which was done, I suspect, because the ignition switch was getting worn out. Again, that's the wire I pulled off the solenoid. The wire to the coil is still attached.

3. When this happened, I was no longer cranking the engine with my momentary button. The engine was stationary. I then turned on the toggle switch to provide +12 to the positive terminal of the coil. I realize if the points happened to be in a closed position then this would fairly quickly start to overheat my coil but I did it just to verify my little LED indicator and switch were working properly. The regular VW horn activated instantly when I turned on the power to the coil via the toggle switch. I cannot imagine how that would make the horn suddenly turn on.

Sat Aug 01, 2020 8:00 am

When the steering lock is engaged it completes the horn circuit, that usually happens when the key is off so it doesn't matter, powering the ignition system from the back disturbs the balance of the universe. :wink:

Sat Aug 01, 2020 8:36 am

busdaddy wrote: When the steering lock is engaged it completes the horn circuit, that usually happens when the key is off so it doesn't matter, powering the ignition system from the back disturbs the balance of the universe. :wink:

Thanks Busdaddy! I did not know that! There is a plenty good chance that steering wheel was turned after we parked it and therefore engaged the steering wheel lock. That would explain exactly what I'm seeing. I guess the easy fix would be do to these things with the key in and turned so the steering is definitely unlocked.

I did wonder if there was some theft-deterrent system installed by a PO that was somehow hooked up to detect this kind of thing but I really did not think it was likely. So this is kind of the VW way of alarming the bus in case someone tries to hot-wire it? (although I never really understood the point of hotwiring a bus to steal it if the steering wheel locks without the key but that's not really my concern right now since it's sitting on my driveway and I do have the key).

Thanks! I will check this today.

Sat Aug 01, 2020 9:44 am

Thanks. I always wondered why when my bus caught fire and some wiring melted, the horn sounded until I disconnected the leisure battery..

I thought it was some kind of death scream.

It only took a day to clean up and get back on the road.

Mon Aug 03, 2020 10:17 am

kinggeorge13 wrote: busdaddy wrote: When the steering lock is engaged it completes the horn circuit, that usually happens when the key is off so it doesn't matter, powering the ignition system from the back disturbs the balance of the universe. :wink:

Thanks Busdaddy! I did not know that! There is a plenty good chance that steering wheel was turned after we parked it and therefore engaged the steering wheel lock. That would explain exactly what I'm seeing. I guess the easy fix would be do to these things with the key in and turned so the steering is definitely unlocked.

I did wonder if there was some theft-deterrent system installed by a PO that was somehow hooked up to detect this kind of thing but I really did not think it was likely. So this is kind of the VW way of alarming the bus in case someone tries to hot-wire it? (although I never really understood the point of hotwiring a bus to steal it if the steering wheel locks without the key but that's not really my concern right now since it's sitting on my driveway and I do have the key).

Thanks! I will check this today.

YOu could add a diode to the stock coil wire to avoid this in the future. Someone smarter than me could give you the correct diode value.

Tue Aug 04, 2020 8:38 am

Since the ignition coil is not fused, and your horn is, you could pull the fuse for the horn while using your hot wiring rig to avoid this in the future.
Or if you remove the hot wire from your coil, you could eliminate the problem of back feeding everything. The downside to that is that your charging system won't work while you test unless you energize the field, so the fuse is probably your best option.