I'm about to mount a passenger compartment heater cable on my Opel Corsa Combo 2015, but I'm a bit unsure how to use the dedicated lead-through.

Under the glove compartment there are two pre-cut holes in the insulation material (one round that seems to fit my purpose, and a larger oblong hole). The plugs in them can be removed and this exposes the steel sheet that is between the cabin and the engine.

It's not totally obvious where these lead-throughs go on the other side of the steel sheet.

How can I make sure where I will end up before if I make a hole in the sheet?

  • I’m curious, what exactly are you trying to do? Repair existing HVAC (Heating, Ventilation, Air Conditioning) or are you introducing new content? From what I know, no manufacturer uses cable through the dash panel designs for HVAC since early 1980’s. Hint: cable controlled coolant valve is a terrible idea.
    – zipzit
    Commented Nov 23, 2021 at 14:33
  • @zipzit, I'm installing a passenger compartment heater. The kind that plugs into 230V mains, so that you can heat the car (to defrost doors and windows) before you use it when it's freezing outside. Commented Nov 23, 2021 at 19:10
  • Crosspost of lifehacks.stackexchange.com/q/25243/6973
    – Chenmunka
    Commented Nov 23, 2021 at 20:42
  • @PetaspeedBeaver Have you considered adding engine block heaters? That may already be available as factory designed parts. Not only will that help with passenger warm up, but will also warm up your engine to get you on your way quickly. Have you looked at existing solutions for cars in extremely cold environments?
    – zipzit
    Commented Nov 23, 2021 at 21:45
  • @zipzit, Yes, I'm installing a kit but will probably skip the engine block heater. To my knowing it doesn't help in heating the passenger compartment, and my actual problem is just that the back doors freeze very easily, so I need to be able to thaw them and am getting tired of jamming the cord for an electrical radiator in the door every time I leave the car :P Commented Nov 25, 2021 at 8:16

2 Answers 2


Lookfor identifying ridges and / or studs or bolts to identify the position then locate that place the other side.

Then drill a test hole with a short drill, check and continue.


One way to identify what is where without the hassle of drilling test holes is to just examine existing content.

Most all manufacturers include a drain at the bottom of the HVAC (Heating, Ventilation, Air Conditioning) system. And that drain may be easy to identify on both sides of the steel dash panel.

HVAC Molded Drain

In this photo, taken from beneath the engine side of the dash panel, the drain is the little stubby molded plastic tube. If your manufacturer offered Air Conditioning as an option, I guarantee, the drain will be there somewhere. In high heat and high humidity, that drain can easily produce four or five cups of condensate (water) per hour (if the operator doesn't have the car in recirculation mode).

On the inside of the car, the drain will be at the bottom of the air handling unit, right beneath the A/C evaporator core.

You can use that location and measure up/down/left/right to determine exactly where to place your pass thru electric cables.

Note, you may well find extra holes/slots in the dash panel in unexpected locations generally sealed with a plastic / rubber plug. Those holes are used to accurately locate the sheet metal in the manufacturing process.

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