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the power windows in my C3 have stopped working. I have been trying to test things by following the attached Willcox Corvette wiring diagram but just found out that one of the previous owners must have rewired the power windows and have bypassed the relay under the console. When I follow the wiring it disappears under the dash and behind the steering wheel.
I don’t have much electrical experience but have followed the Willcox wiring diagram and have tested:
- The 30 amp circuit breaker on the firewall in the engine bay (labeled A on the wiring diagram) and there is power.
- I have tested the fuse box ( labeled G on the wiring diagram) and there is power.
- I have pulled power from the battery and checked that the switches and the wiring to the windows and everything works.
I just can’t work out where they would have pulled the wiring after bypassing the relay.
Has anybody done a similar thing or come across something g similar?
Would appreciate any help and tips on this.
Thanks in advance
Last edited by Tofigh; Mar 11, 2026 at 04:26 AM.
Reason: To better describe the post
Can we assume the wiring between the switches and the motors in the doors are not modified? Also, the up/down console switches have 3 terminals and should have 12V on the middle terminal when the ignition is on.
I have taken off the passenger side door card couple of years ago and it had the original wiring. The switches are three pin, I tested them with 12 volt power from the battery and they work and I can operate the windows. Without me supplying power to the switches from the battery, there is no power to the switches and that is what the problem is. I am not getting power to the switches, otherwise everything else works.
I took another look under the bonnet this morning to find the relay labeled C in the Willcox diagram and see there is another relay sitting beside it and seems to be aftermarket (photo attached) and
not sure if that provides any clues.
That relay is NOT factory!!! Not insulated- is just plain scary!!! Fire hazard as it also is using wire not rated for underhood use ( AKA "primary" wire - melts at 180º not oil/gas rated- need "SXL" type)
Looks like they have re-wired the power source for the power windows- badly!!! Looks like they also bypassed the circuit breaker (A-B in the picture)
Just because the factory wiring is/looks correct in the door-
A common solution to mostly repo windows switches burning up- or
not switching power very well-
A couple relays ( done correctly) solves the problem.
Here's this diagram I did years ago- relays would be inside the car- console more than likely.
Will require 4 relays- just showing right motor upgraded
Ok, on that relay you found in the engine bay, the 2 terminals 87 and 30 are the 12 source going back to your console switches. Check those first and verify that you 12 volt on at least one of those 2 lugs. One of them is likely double terminated over to 85 or 86 but you can ignore that for now.
I have tested the relay in the engine bay. The terminal that I have labeled H in the attached image is 12.5 v and gets it power from the either a circuit breaker or the replay mounted behind it ( by the vacuum tank shown a J which flows through a fuse labeled I.
I have traced the two cables that it feeds. They feed the two horns and the electric fan in the front so I am not sure that it goes back to the console.
back to the console for a minute. On the up/down switch in the console there are the 3 terminals. If you connect the center terminal to either of the other 2 terminals with a short jumper, the window should go up/down. This assumes 12V is on that center terminal
The highlighted area is where the main power goes to the windows. I don’t get any reading at this point. If I bring a 12 v to this point from the batter, then the windows operate fine. That is why I think the window motors and the switches are fine.
So your window switches are fine-
And the relay under the hood is for your fan- but I would definitely redo it correctly...it's just an unsafe fire hazard
The relay that is disconnected is so your windows only work with car in ignition.
When your windows previously worked- did you have to have the ignition on?
You need to trace the wire from the circuit breaker- as its hot - albeit protected by a circuit breaker-
Last edited by Richard454; Mar 14, 2026 at 02:58 AM.
Thanks for the advice Richard, I completely agree that it needs to be made safe. That will be the next step. At the moment, I am trying to figure out how the wiring works.
Before it stoped working, I had to have the ignition on for the windows to work.
At the moment, I am trying to figure out how the wiring works.
Before it stopped working, I had to have the ignition on for the windows to work.
The somebody has either added a relay ( best ) or wired it directly to an ignition wire- not as good-
As there are no circuits left over can be been tapped on- to handle the amount of current the windows pull.
The circuit breaker is needed -as the power windows when hitting stop points -current spikes- if you had a fuse the possibility of blowing it would be too high.
Thus they used a circuit breaker to reset before the wire gets damaged - melted..
My guess-
There is a fuse that was added in line that has blown- or look closely at your fuse block for a blown fuse if they tapped another circuit.
The wire isn't shorted pout- as when you put power at the console- you didn't see sparks.
You could simply go to the battery- put a 30A circuit breaker- run 12 gauge wire and splice the wire under your console- the windows will operate without the ignition on-
They will run better/quicker as they have a shorter/better wire run.
Best way - add a relay to switch on with the ignition.
Thanks Richard. I like the way you have explained it. I will drop the steering wheel down and have a look at the ignition to see if I can trace the current wiring but the solution you have recommended is really good and that is the fix I’m going to apply.
Another thing to consider is the wiring from the body to the door. Considering the flexing that occurs every time you open and close the door, the harness running between the body and the door may cause one or more wires to break inside the flex tube. The insulation hardens over time and does not flex. The insulation cracks and the copper wires will bend until they break. Sometimes you can move the flex tube out of the way enough to inspect the harness..
Power windows wiring help needed
