Cure your VW Starter Blues!

Starter-solenoid Trigger-voltage Booster-relay

The STBR cured my 1984 VW Jetta warm start problems. Disclaimer: I am not responsible for any damage to you, your car, or occupants of your car arising from the use and/or misuse of these instructions.

Symptoms: Car starts normally when cold, or up to about 15 minutes of operation; after reaching normal operating temperatures, the starter solenoid will not engage (no cranking) until the car cools down; jump starts from a good samaritan will miraculously get the car started, but you know the problem is NOT with the battery.

Cause: The starter solenoid trigger voltage drops below 9 volts when engine is hot; jump starts work because voltage from a running engine rises to around 14 volts, elevating in proportion the solenoid trigger voltage. The trigger voltage comes from the battery, to the ignition switch contacts, to the automatic transmission lock-out switch (which allows starting in Park or Neutral only), and finally to the starter solenoid; any one of the switch contacts in this circuit could have aged to the point they are now susceptible to temperature changes. As temperature rises, electrical resistance rises; by Ohms law, as electrical resistance rises, voltage drops.

Verification and temporary fix: To verify that low solenoid trigger voltage is the cause, connect a wire to the starter solenoid trigger connector, and briefly touch the positive terminal on the battery with the other end of the wire; the starter solenoid should engage even when the car is hot; DISCONNECT the wire from the battery (leaving the starter solenoid trigger connected for more than 30 seconds can burn the starter motor!). You can start the car if you put the ignition key in the ON position, while briefly connecting the wire to the battery; insulate the end of the wire with electrical tape so it doesn't accidentally crank the starter.

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Quick and dirty cure: Install a STBR, which connects the starter solenoid trigger wire to the battery terminal whenever you have the ignition key in the START position. a) get a headlight relay (Radio Shack 275-226); b) connect the ignition switch terminal coming out of the firewall to the headlight relay trigger point; c) mount the relay to the firewall, and ground the relay; d) connect the starter solenoid trigger connector to one of the switching contacts of the relay; e) connect the remaining switching contact to a fused 12 volt source (use a 10A fuse). (Refer to schematic diagram)

The real cure: Find out which switching contact is susceptible to temperature changes, and replace the switch(es). The problem is most likely to be with the ignition switch contacts, so you may have to change your ignition key(s) if you don't want to replace the lock mechanism. The transmission lock-out switch is the less likely culprit, and is located under the transmission selector cover; when the car is hot and will not start, carefully bypass the lock-out switch contacts to see if this fixes the problem; I strongly advise against leaving this safety bypass in the car.

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