Electric window relay problem

Please can anyone help with this one.
My brother's 1994 C180 has gone through four batteries, after failing to start up.
He had the Alternator tested, and it was found to be ok.
After having the car looked at by two auto electricians, he was told there was a problem with the relay for the electric windows.
He tried a new relay, but it was still the same.
As soon as you plug the relay in, it clicks. ( indicating a permanent connection somewhere along the line )
When he got the car, neither rear window was working, so he took the motors apart and fixed the brushes.
All switches and motors seem to be working perfect.
To try and find the problem, he's disconnected the cables to the rear doors (switches & motors ), but the relay is still getting power permanently sent to it from somewhere else.
Anyone have any idea on what else to look at ?
I noticed that when he activated the windows, there was a clicking noise from the black box at the side of the battery, but we haven't looked at that yet.
Any help would be greatly appreciated.
John
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The purpose of the relay is so that there is no need to draw big power or heat at the switch when in operation. So the relay always have power from the fusebox.
Your way of diagnosing the problem is wrong. It may not even be the windows. What you need to do is chech the voltage when enging is running.... with RPM at about 2000 RPM, you should have 14V or slightly higher... 14.4 is the best. At idle, you should have at least 13.5V.
If above is okay, then you need to check the draw of the battery when ignition switch is off... disconnect the battery at negative. Use a multimeter set to DC Amp... connect it between the negative battery and the negative battery cable. if it is like 1 amp or lower, then it is fine. If it is higher, then you need to go to the fusebox and take one fuse out at a time to see if it is the culprit. If not, then put it back and go next one.
Another note, if you have aftermarket amplifier or stereo system, you need to verify that first... Some so called pro have no idea what they are doing and put amp on all the time. Same goes for alarm system,
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Have you tried disconnecting the console and/or door window switches to see if one of them is stuck closed and activating the relay. It sounds like you have 12volts going to the relay coil all the time when you want nothing. That's what you need to traceout.
--

73
Hank WD5JFR

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To try and find the problem, he's disconnected the cables to the rear doors (switches & motors ), but the relay is still getting power permanently sent to it from somewhere else.
The "somewhere else" could be a (stuck) switch on the console between the front seats. These often get dirt (and soda) in them and stick - in this case ON.
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