window rollup module basics

howie ll wrote: It just occurred to me that if the power supply sits at ground with the ignition off and you only use the window closer with ignition off, you won't need a relay since all the wires will be at ground.

Odds are the power wire doesn't sit at ground when the ignition switch is off. It just shows a path to ground through other stuff that sit on the same circuit. '83 Mercedes, come on now it's about time to move into the modern era, after 31 years, and buy a new car with window roll-up and other amenities built-in.

catback wrote: '83 Mercedes, come on now it's about time to move into the modern era, after 31 years, and buy a new car with window roll-up and other amenities built-in.

hmm...I'm awaiting Windows 9? Actually the diesel 300SDs and similar models are legendary and sought-after for their longevity, eg 500K miles and much more with reasonable maintenance - to say nothing of their tolerance for running on alternative fuels with little or no modification (waste vegoil, for example). I do wish I could buy a 2014-anything that could do the same, especially something less than 17' long.Dave

Catback's, bet it does sit on solid ground, test and if so worth a try but I don't really care I must have 100 relays lying around. Pants, your absolutely right I've worked on two recently, both owners have had them from new and commented on NO COST running.

Thank you Howard. "It just shows a path to ground through other stuff that sit on the same circuit. " means it is at ground. How grounded? - add up all the parallel resistances, or try grounding a 3W or 10W or 55W or 100W bulb thru turned off IGN.

In my case, at least, no, there's no chance ground available by just keying off - though I'd love to find an even easier way around this, so I'm attaching the musty old schematic and maybe someone will see something I don't/can't. I think Catback might have been referring to the "impression of a ground" that you'd get from an ohmmeter reading through, say, a filament of an indicator lamp that happens to tie into that hot-lead - and thence to ground. But try to USE that lead as a ground with a low-impedance device like a window-motor, and most likely all the voltage drop will be across the filament. Dave

Have you tested that power supply (supplies) to the window switches (can't read your too small diagram), I'm sure one is BLACK / YELLOW with a DMM with the ignition off? In other words both motor wires to each motor should rest at ground.

With old vehicles there was a reasonable chance of a 2-4 Ohm GND thru the IgCoil alone. But as Howard suggested - TEST. The number of times we have used phantom- or pseudo-grounds like this for anything from LEDs buzzers & relay coils to lamps of reasonable current. And if it can actuate a relay coil...