Hello, My bus a 79 2l type 4 has got a petronix flamethrower 3 SVDA a matching coil, new sparkplug leads and plugs. I read somewhere that the electronic points may not work properly unless they get at least 12V. Since my bus is not running as I would like I decided to power the coil which feeds the distributor from a 4 pin relay fed via a fuse directly from the battery and triggered using the old coil feed from the ignition switch. I tested the circuit and all seems fine, when the ign switch is off there is no voltage on the old black coil feed, when you turn on the ignition there is 12v on the old coil feed and this brings in the relay as expected and the 12v direct from the battery feeds the HT coil. All these tests done with the engine not running. If the engine is started to a slow tickover (which doesn't turn off the ign light) and the key is turned off the engine stops as expected. If however the engine is started and revved up a bit so the ign light goes out when you turn off the key the engine keeps running with the relay still energised. When in this state with the engine running and the ign key off I can measure 3V on the black wire the old HT coil feed which now goes to the relay coil. It seems 3V is enough to keep the relay closed. If I break this connection to the relay coil the relay drops out, the engine stops and the 3V disappears. I don't understand where this voltage is comming from so I wondered if anyone can explain it. It appears that there a voltage on the black wire from the ign switch when the engine is running and the battery is charging but the key is in the off position.
I would suspect your ign switch is knsckered, or someone has "improved" the wiring at some point. Adding the realy won't achieve anything, btw. I'd remove it.
You have answered your question. The current through the alternator warning light is enough to leave three volts on the ignition + rail under the dashboard. And that holds the relay on. One way out is to connect a resistor across the relay coil to reduce the voltage until it drops out. E.g 120 ohm 2 watt resistor .. will take it down to maybe 1.5 volts Or use a different less sensitive relay.
If it doesn't work if the supply drops below 12V, then it does need to go in the bin. But if there's not a reliable 12V at the coil, I'd go for wiring or ign switch. Shouldn't be 3V on it with the ignition turned off (if I understand correctly).
Found some kind of a workaround. If I load the original ign wire with the feed to the automatic chokes and solenoids and only power the coil and distributor from the relay then the engine shuts off with the key. It's like the load of the chokes pulls down the voltage to the point where the relay won't stay on. I'd still like to know where the 3V was coming from though.
There is a problem with the Type 4 engine that the stock wiring to the coil is thinner than the Type 1 so the voltage dips even more as the ignition draws current. The Pertronix Ignitor 2 is slightly affected by this..(analog electronics problems) .. the fancy and expensive Pertronix Ignitor 3 has this and other (software? ) problems. Like if its idling lumpily, the Ignitor 3 makes it worse.. If it idles like a bag of nails but pulls brilliantly, its quite possibly the Pertronix electronics. So fitting a power relay for the coil power is a good idea to smooth out the maybe 1 volt dips on the coil positive in a Type 4 engine ( its about half that drop, about 0.5 volts on my T1 e.g... so Pertronix probably were playing with a Beetle that could rev to 9000 rpm and which idles lumpily on a racing cam, so the Ignitor 3 didnt change much..)
Yes , this fixes it by making sure the ignition feed from the switch is not maintained at 3 volts by the current through the alternator warning light. On some Beetles, there was enough voltage on the coil for the engine to keep running in this state. Where aftermarket carburettors no longer have choke heaters or cutoff solenoids..
Thanks for your replies it makes sense now. I thought that when the ignition switch was off then the black wire feeding the coil was totally disconnected but clearly this isn't the case and the alternator current is capable of creating a voltage on the wire. Your right my bus idles like a bag of nails but it doesn't pull briiiantly either! I can hardly get it up the hill to my house. I'm not sure my relay mod has made any difference, think I might get a 123 distributor instead. Wish I could get it to work.
With the ignition off, the black wire should be completely disconnected. You need to find out why yours isn't as a first step. Binning the Pertronix would be a good thing to do.
Actually the modern digital meters draw currents of 0.0000001 amps to measure voltages so if there is leakage across a switch connected to 12 volts and the output wire is disconnected from anything you see a voltage greater than zero on the output wire. An expensive Fluke meter will also show voltage in this case. This voltage reported by the OP will be a genuine three volts , the relay coil will be about 100 ohms with 0.03A going through it fed by the warning light .. which is a 12 volt 0.1A bulb with around 9 volts across it. As for a solution, I would go and try an inexpensive points based distributor to check/prove theres nothing wrong elsewhere.. and then keep it ;-) Or find a Bosch and buy a couple of cheap points replacement modules to fit ..avoiding distributors where the manufacturer sells you an overpriced package of Chinese distributor and Chinese module with a sticker on it. The £40 eBay modules are OK and fail the same as expensive ones... Or if you feel you need to spend on it, buy a 123...
Good idea. I don't know why folk sell these things. Can't go wrong with a 123. But...you'll still need to sort your wiring/ignition switch. Something's not right somewhere.
Its the relay intended to provide a direct battery feed for temperamental electronics.. that causes the strangeness in the first place.
