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Adding relays to my Power Window circuit

36K views 19 replies 4 participants last post by  EOD Guy 
#1 ·
Hi:

I have an old set of Autoloc PWs and they're not getting enough power.

I want to add relays to fix this and have a couple questions:

1: There are two wires going to each motor--one powers up and the other down. I assume that I just put a separate relay each of these wires--ie that the PW window switch will now operate the relay instead of sending current directly to the motor.

2: I don't understand how the motor is grounded. I assumed that it was just grounded by being bolted to the door, but when I took the motors out and laid them on the floor, they still functioned. Does anyone know how this works and if introducing the relays into the circuit will mess up that mystery ground?

Thanks!

Kyle
 
#2 ·
The two wires are not one up/one down with a separate ground. They are power and ground, and the switch reverses the connections to change direction. GM has used this wiring scheme since the 1980s and probably even earlier. You need two relays for each motor, wired like this:

 
#4 ·
It's called a reversing relay circuit. the common terminals on the relays are connected to the two motor wires. The normally closed terminals are both connected to ground, and the normally open ones are both connected to power. The window switch operates one of the two relays for up and the other for down. When you energize one of the relays, the contact moves from the ground to the power, and the other (non-energized relay) stays connected to ground. This powers the motor in one direction. Pressing the window switch the other way reverses that and powers the motor in the other direction.

Factory PW relays have this dual relay circuit built into a common housing, but they probably cost more than just using a couple of the generic relays per window.

This shows it more graphically.

 
#5 ·
Actually, I take it back. In looking at that diagram, 85 and 86 appear to be connected to the wires currently running from the switch to the motor.

But what is the wire coming off the the one connecting the two 87s to the battery? Is that going to another wire on the two way switches that controls the neutral (off) position? I recall those switches each having 4 terminals.

Thanks,

Kyle
 
#6 ·
EDIT (fixing a typo):

If the switches have four wires, then they are doing the reversing in the switch. I assume the four wires are power, ground, and the two motor wires. The switch works by applying power to one motor wire and ground to the other. Take one of those switch wires that would previously have gone to the motor and run it to one of the relay control terminals. Run the other to the other relay control terminal. Note that terminals 85 and 86 are the two ends of the control coil in the relay. So long as one is connected to power and one to ground, the relay energizes. It doesn't really matter which is which, and apparently in my first diagram, they have used both 85 and 86 for both control and for ground. Again, this doesn't matter. The 87 (power) and 87A (ground) are the terminals that will power the motor once the relay is energized.

When the relays are both off, both sides of the motor are connected to ground and there is no current flowing. The battery is only connected to the normally open relay terminals and makes no connection until you energize one of the relays with the switch. Actually, if you were to accidentally energize both relays at once, you'd get 12V on both sides of the motor and still no current would flow and nothing would happen. The motor only operates if ONE of the relays is energized.
 
#8 ·
Thanks. I think I'm starting to wrap my head around it.

Because they relays are connected and both have ground/power, it means that if neither relay is activated, they're just two grounds. No circuit. If both were activated, you'd have two hots and no ground. Again, no circuit. Only when one is activated do you have a ground and a hot. This creates a situation where the ground/hot wires change roles depending on the position of the rocker switch.

Now, can I translate that knowledge into windows that actually go up and down? This remains to be seen. :D
 
#9 ·
You have the basic concept

When two relays are used

Relay 1 - Normally Closed (NC) terminal is connected to ground.
Relay 2 - Normally Closed (NC) terminal is connected to ground.

Relay 1 - common terminal is connected to one wire from the motor (let's say White for this example)
Relay 2 - common terminal is connected to one wire from the motor (let's say Black for this example)

Relay 1 - Normally Open (NO) terminal is connected to a hot 12 volt source
Relay 2 - Normally Open (NO) terminal is connected to a hot 12 volt source

Relay 1 - Coil terminal 85 is connected to a ground
Relay 2 - Coil terminal 85 is connected to a ground

Relay 1 - Coil terminal 86 is connected "up" side of switch
Relay 2 - Coil terminal 86 is connected "down" side of switch

When the Up side is pressed.... Relay 1 energizes and switches the Common contact (White wire from motor) from the NC contact (Ground), to the NO contact (12 volts). This allows 12 volts to flow thru the relay, thru the WHITE wire, to the motor. The Black wire from the motor is connected thru, Un-energized Relay 2 to ground....... motor spins clockwise.....window goes UP

When the Down side is pressed.... Relay 2 energizes and 12 volts flow thru the relay, thru the BLACK wire to the motor and the White wire gets grounded thru Un-energized Relay 1......... motor spins counter-clockwise........window goes down


With non-relay system the up/down switch does all the reversing etc......
 
#10 ·
"set of Autoloc PWs and they're not getting enough power." What makes you think this? If there is a main power wire that runs them connected to an iffy power source adding the complication of relays won't accomplish a thing.
You might try jumping a wire directly from the battery to that one single power wire that feeds the switch(es)and see if the windows work better. If not then find the one main ground wire and try jumping it to a better ground. Voltage drop testing with a multimeter is what's really called for here, but jumping wires to better connections will hopefully be enough to help you find the issue.
 
#11 ·
I initially thought it was a combination of a tired old motor and loose bushings that caused the window to bind.

However, part of my trouble shooting was to connect a hot directly to the motor from the battery. The windows shot right up.

In truth, a new PW kit wouldn't be a bad idea, but man getting those things in and out of the door is a pain...


km
 
#13 ·
So you don't need all that jazz with the relays, just a better power source hookup than you have now.
Of course one way to do that would be a direct line from the battery to a relay then power everything off that. No need for a relay to each motor. But really just a better main connection should do it.
 
#14 ·
I'm not picturing how that would be wired.

Basically, I have a really long run of narrow gauge wire (from the fuse box to the cheapo switches to the window motors) causing voltage drop.

Four relays (up/down right/left) allows me to create a short run of 12 gauge directly from the battery.

In theory, a cheap and easy solution. In practice? We'll see... :rolleyes:
 
#16 ·
Well, I'm not picturing how a handful of relays will fix a base power problem. How about you replace that long run of "narrow guage" with a run of big fat wire, temporarily, straight to the battery. If that fixes your problem then you just need a better wire AND a better power source. Which is what I really suspect your problem is. You don't want to get silly complicated with relays all over the place only to discover that was all you needed to start with. Right?
 
#17 ·
I have done what you suggested--ie run a fat wire from the battery direct to the window. It did fix the problem.

Replacing the narrow wire with a heavier gauge would be really difficult because a lot of it is under the carpet.

I'm not sure what you mean by a better power source. A new battery? :confused:
 
#18 ·
Regardless if you use relays or not, you need to run a new power wire to feed them (rather thru them). I'd run a single 12 gage (10g if you plan on adding more stuff later) wire from the positive post on the battery to up under the dash area. From there you can feed the relays etc....... or if you prefer, straight to the switches etc......
 
#20 ·
That's correct, using relays, the switch will only provide power to the relay coil...... trust me the coil will fry long before the OEM will melt....lol.

I removed the drivers side toe-kick panel and mounted the relays in the void, The wire running thru the pass thru was already in that area. I ran new 12g Wht and a Blk from the relays to the motors, mine were crappy and I wanted to replace them. My power wind and locks are on separate fuses in the fuse block, if your's aren't I'd suggest placing a 30 amp C/B between the pwr supply wire and the relays.
 
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