It's a function that's so common on modern cars it barely merits a mention: variable delay for the intermittent wipers. Older cars often don't have the variable delay, but many of them can be upgraded very simply.

All you need to do is swap the relay that controls the wipers for the Volkswagen relay shown above – commonly known, for obvious reasons, as a '99 relay'.

What you need99 6337

  • A vehicle with intermittent wipe with a fixed delay, using a relay like the one shown on the right to control the wipers. In this case the vehicle is my 1994 Land Rover Defender.
  • Volkswagen '99' relay, part number 357 955 531. You should be able to get one new for £10 or less.
  • Any tools required to gain access to the relay – all I needed was a screwdriver.

How to upgrade

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  1. Make sure the windscreen wipers are switched off. It's a good idea to remove the battery earth lead to make sure you can't touch anything that's live.
  2. Find the wiper control relay, which may be in the fuse box – as in my Land Rover.
  3. Check that the original wiper relay is of the same type as the red one shown above.
  4. Swap the old relay for the new '99' relay. In the Defender I had to unscrew the bracket holding the relays and fuses to get access to the relay and its plug.
  5. Replace the fuse box cover and reconnect the battery as necessary. 

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How to use it

  1. Switch the wipers to the intermittent setting - the wipers will start to sweep the screen as normal.
  2. Before the wipers return to the park position, switch them off.
  3. Wait, then switch the wipers to intermittent again.
  4. The wipers will now work intermittently, using the length of time you waited in step 3 as the delay time.
  5. To reset, repeat the process.