Starter Circuit


copyright 2004 dragenwagen


Ever get into your VW and it won't start?

Turn the key and nothing happens?

All it does is click?

It happens at the most inopportune time, doesn't it?

Now do you understand the starter circuit? Do you know why it won't work. Hopefully this article will help.

If you have a decent understanding of basic electrical properties this will be easy to understand. If not, then then I will try to make it simple as possible. First off lets assume that the battery has a good charge on it and your charging system works like it should.

Batteries that are 3 or 4 years old should be replaced, depending on the quality of battery. The acid in a wet cell car battery breaks down the lead plates inside the battery. The sediment that collects in the bottom of the case shorts out the plates and that is why they go bad.

The diagrams below are for a 1968-69 Beetle... so the wiring may differ slightly on different years and models, but the concept is the same.

I have simplified the wiring diagram to show the starting circuit -

Starter circuit simplified even more -


And yet a more detailed diagram -


So now we have a picture of the system, but it doesn't solve the problem of why it won't start when you turn the key. Lets look at what should happen -

When you turn the key, the electrical current operates the solenoid in the low current circuit side of the starter, this is to prevent arching of the contacts in the ignition switch . This is so you don't have a heavy gauge wire going all the way up to the dash, which would cause a voltage drop, also the ignition switch wouldn't last very long.

When the solenoid operates, it pulls the rod and the copper bar in the solenoid. The copper bar will close the contacts of the high current side completing the circuit. It will also kick the starter gear out to mesh with the flywheel on the engine. Then the high current needed by the starter motor will flow, turning the starter motor which will in turn turn over the engine.

When the engine starts, you back off the key and the current in the low side stops flowing, and the solenoid is released. This release pulls the copper bar away from the high current side contacts ( with the aid of a spring) and the starter motor stops as gear pulls away from the flywheel.

Simple right?

So why won't my car start?

The ignition switch - the ELECTRICAL part not the mechanical part will get pitted or have corrosion in it after many years of trouble free starts, but like all things electrical or mechanical, they do have their limits, and it will simply need to be replaced.
The wiring Bad wiring can be a troublesome thing to find and deal with. The wire or the connectors anywhere in the system can be corroded, loose, insulation cracked, splices, bad crimps. Any of these things can cause a bad connection or simply cause a voltage drop to where you don't get the full 12 volts to the solenoid!

Check and clean all contacts! especially on the starter and solenoid.
The solenoid (copper bar) There is a heavy copper bar inside the solenoid that closes the high current circuit. We all know copper corrodes easily, especially in damp conditions.
  I have successfully taken the starter solenoid apart (which requires you to unsolder the electrical contacts with a big soldering iron and taking out some screws) and using some fine sand paper to clean the copper bar.
Solenoid contacts Also where that copper bar touches the high current contacts - they tend to pit over the years and after a while the copper bar will not touch the contact any more... that means the circuit is not complete and the starter will not turn!

Time for a new starter at this point.

Note: If you get no clicking noise when you turn the key it might be the switch or the wiring in the low current side.

If you hear the click from the starter then there may be a problem in the solenoid or starter motor.

Do not turn the key and hold it into the start position for too long, as you can burn up the wires that go back to the solenoid. Yes it happened to me and I had to replace the wire going from the switch to the solenoid. ( melted off the insulation...doh! )

There is one more culprit - starter bushing!

Starter Bushing - VW starters are unique, er um weird...

In a standard 4 speed manual transaxle the starter it self doesn't have a bearing supporting one side of the armature. Duh - pretty stupid IMHO! So when the starter gear pops out to mesh with the flywheel, the end goes into a little sleeve in the transaxle housing. That's what supports the other end of the starter shaft. When you buy a new starter, it should come with this bushing. This small part can be a pain to put in. I usually have the engine out and the starter removed.

Temperature will affect this part, preventing the shaft from going inside, or if it becomes worn out or distorted, the motor windings can short out.

However - autostick shift models have a starter with a bearing in the starter itself and they usually have a higher output.
   BTW if you take your 4 speed manual starter to Auto zone to have it tested.... forget it, they won't because with out the bearing it may damage the starter.

I had a 68 Beetle, when I was younger, that was notorious for no starts. I would turn the key and nothing happened or the starter would just click. until I really understood what was going on with my starter I would use a screwdriver to start it. So what does that mean?  
I have successfully started my beetle by placing a screwdriver from the big wire coming from the battery to the connection on the solenoid...

You get some sparks and the starter ususally kicks over...

SO make sure it is out of gear
and the key must be in the ON position if you want it to start.

Essentially the same method -

But you can try to jumper Terminal 50 on the solenoid to the + side of the battery to see if the starter will work.

AGAIN make sure the car is out of gear and the ignition must be ON if you want the engine to start.

There have been discussions on putting a hard start relay in the starter circuit. But it is just a band-aid. It's just covering up some other problem in your starter circuit, and sooner or later you will have more problems and the car still won't start like on my 69 beetle...

So there you have it. The basics of a VW starter and what some of the causes might be that prevent you from starting your beetle.


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