Ford Mustang: Blocked cowl drains flooding the passenger footwell and junction box

Leaves and debris collect in the cowl at the base of the windscreen, and when the drains block the water backs up and finds its way into the passenger footwell. That would be a damp-carpet nuisance except for where the smart junction box sits: water reaching it produces electrical faults that are expensive and maddening to chase, because the symptoms appear in unrelated systems. On a car of this age in New Zealand, where cars sit under trees and rain is frequent, this is worth checking on every example. Clearing the drains is free; replacing a drowned junction box is not.

• Damp or wet passenger carpet, or a musty smell inside
• Windows, locks, lights or interior electrics behaving erratically
• Water heard sloshing behind the dash over bumps
• Fogging inside the windscreen that will not clear

1. 1

   Press the passenger footwell carpet firmly with your hand, right into the corners and under the mat — damp is what you are looking for, and a car that has been aired out for the viewing can still be wet underneath.

2. 2

   Lift the mat and check the underlay.

3. 3

   Smell for damp or mould with the doors shut for a minute.

4. 4

   Open the bonnet and look at the cowl area at the base of the windscreen for packed leaves and debris, and check the drains are clear.

5. 5

   Look for rust or water staining low down on the passenger side.

6. 6

   Inside, test the windows, central locking, interior lights and indicators for anything intermittent.

7. 7

   If it has rained recently, so much the better.

8. 8

   If a workshop inspection is possible: have the smart junction box area inspected for corrosion, since damage there is what makes this expensive rather than annoying.

$100 to $2,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the passenger carpet ever been wet?”
• “Have the cowl drains been cleared, and how often?”
• “Have there been any odd electrical faults?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.