Plus 2 window wiring mystery

[The Veg]

Taking up from my thread about the window in the chassis/body section, I have a window that will go down but not up and the problem seems to be electrical.

After disconnecting the wiring in the door from that in the dashboard, I found two things to be true:

1) The switch functions properly, delivering full voltage to the wire that corresponds with either side of the switch.

2) Using a jump-lead connected to the hot side of the starter solenoid, the motor can be operated in either direction by touching the jump-lead to the wires that go into the door, making the window lower or rise without hesitation.

But then with the dashboard wiring re-connected to the door wiring, the window will still go down but not up, which makes no sense based on 1) and 2) above. Downright contrary.

I recall in past forum-discussions there was plenty of advice to use relays for the window power, which should in theory solve this but the fact that this electrical mystery happened at all still bothers me.

[alan.barker]

Has the Switch got high resistance on one contact.
Alan

[HCA]

Just to be clear, as it was not in your last post - you have the motor back in place and hooked up to the window mechanism, but with a jump lead bypassing the switches, you can get the window to operate both up and down without any trouble, Yes? And the 'down' switch is perfectly ok, yes?

With the jump lead bypass, you can send the window all the way to the top and the limit switch kicks in, yes?

If a definite yes, yes and yes, then it is the 'up' feed and/or switch.

Relays are a hindrance here if everything is assembled correctly.

[chris57]

Have you considered voltage drop across the switch contacts?

If you checked the voltage with no load (motor disconnected), the voltage may be OK but, add the load of the motor to the circuit and any high resistance across the switch contacts (or relay, if fitted), would cause a voltage drop.
Try putting a voltmeter (low voltage setting) across the switch or relay contacts with a helper operating the window.
If there is high resistance a reading will be seen. A perfect low resistance contact would show no voltage.

Another simple way would be to short the switch with a link.

[john.p.clegg]

... or easier, connect one leg of your voltmeter to a good earth ( not easy in a Lotus ) and probe around whatever points you can get to in the circuit , while operating the window up/down.

Post the results for a diagnosis

John

[The Veg]

Just to be clear, as it was not in your last post - you have the motor back in place and hooked up to the window mechanism, but with a jump lead bypassing the switches, you can get the window to operate both up and down without any trouble, Yes? And the 'down' switch is perfectly ok, yes?

Yes.

With the jump lead bypass, you can send the window all the way to the top and the limit switch kicks in, yes?

Yes.

If a definite yes, yes and yes, then it is the 'up' feed and/or switch.

Each component of the up-circuit tests fine by itself but when all are connected, nothing, and it started suddenly during the last drive.

Poking around more with it I've been unable to find any more clues.

Relays are a hindrance here if everything is assembled correctly.

I must disagree. Tonight I did a test with a relay left over from some other project, used the jump-leads to feed a it from the hot side of the starter solenoid, and with this setup the window arose with MUCH more authority than with the original circuit, just like when I used the lead to run it directly. More direct power than what comes through all the convolutions and connections (losses) of the original circuit that also supplies everything in the dashboard, which stands to reason since I also saw an improvement when I ran the motor's earths direct to the chassis instead of through the dash-loom back when I renewed the motors a few years ago. The bottom line is that with power fed from a more direct source than what comes from the switch and related wiring the window moves like in a modern car, no struggle at all. Probably better than when new.

[HCA]

My emphasis is on the pure meaning of 'everything assembled correctly'. This does not necessarily mean 'how the car might have left the factory'

The only reason for a relay in such as window wiring, is to reduce the size of cabling and switches. They are purely there so the manufacturers can save on the switch and cable costs. Bear in mind that if a manufacturer can save a buck on cabling in one car, this is a million bucks on their total run.

You proved it yourself by using jumper leads to test. Big thick copper cores, that is what the motor wants to see! A few metres of 4mm2 thinwall in your Elan is, unlike to a manufacturer, nothing to worry about and less faff than a relay.

[Bud English]

The weak link in the window circuit is the fifty year old appliance switch that was originally designed to switch a high voltage, relatively lower amperage, motor on and off. These weren't originally 12V DC automotive switches. ...but they were cheap (and they will handily switch a high amp 12V relay coil).

[Slowtus]

HCA has it in a nutshell and without going on at length about resistivity, conductance rho, l and A etc - fling in a fat wire, problem solved.

[The Veg]

You proved it yourself by using jumper leads to test. Big thick copper cores, that is what the motor wants to see! A few metres of 4mm2 thinwall in your Elan is, unlike to a manufacturer, nothing to worry about and less faff than a relay.

Maybe my choice of words wasn't good. By 'jump leads' I meant wires with alligator-clips at either end- but they're small, about the same gauge of wire as the existing circuit. You must have thought I meant the big leads for jump-starting a car...no, nothing that big.

So the original mystery was never solved but the relays I added made it a moot point.