bench test pw motor
 

1978 Silverado I just bench tested my pw motor. You test by connecting one to positive the other to neg. reverse them to reverse motor . I think I got this figured out BUT not really. The way my 78 works is with 3 wires off the switch. Most I have seen on utube have four. This lies the issue. With the four wire the 4th wire is a ground and it fills the circuit of the opposite side of the switch with a ground so when you push the switch the switch lets power to one side and ground to the other. My problem is I dont have that 4th ground wire, So when I push the switch I get power to one side but no ground to the other and when I push the switch the other way the power goes to the other side but no ground. I do have a ground wire coming out of each door harness ( I grounded to each door frame)and one that connects to the firewall area but can't figure how the motor gets grounded. Thought it was the switch but I tested for ground on the front side with no good results. Anyone know how these three wire switches get ground to the motor? Thanks

Re: bench test pw motor
 

Are you thinking your switch does not have the 4th wire broken off or disconnected? Let's see some pictures of the switch.

Re: bench test pw motor
 

here's is what I got. 3 wires to switch and switch seems to have only 3 contacts on pass side and drivers side is without a ground also.

Re: bench test pw motor
 

Attachment 2044811

Three wires one in middle (Pink) is ign Hot One on each side go to motor. no ground anywhere that I can see,

Re: bench test pw motor
 

drivers side

Attachment 2044812

two blues two grays a set for each motor
Red for ign power

dont know how I can get ground off this switch when no ground goes to it. Pretty sure in 78 its was a first design from wat I can tell.. second design had the 4th wire.

Re: bench test pw motor
 

drivers side

Re: bench test pw motor
 

That is interesting. Perhaps it gets ground from the metal tabs where it is inserted in the door, that is my guess. If that's the case I hope the door has a ground strap and doesn't just rely on the metal hinge.

Re: bench test pw motor
 

According to my wiring diagram the early models only put power to one wire or the other. The motor itself is grounded to the door by the bolts. Later models reverse the polarity and are grounded through the switch.

Re: bench test pw motor
 

I am leaning toward the motor grounds itself to the door as I do have one ground wire in each door harness. I am starting to think the motors are the newer type and my harness is the older type. One more interesting thing. There are two different motor pigtails ( harness plugs) on each door. It may be someone added the power windows or tried to put the incorrect motors in at some time. I am going to my local c10 parts place tomorrow and ask to see the difference in the two different motors. I bet the connecting plugs are the difference. if so I will buy the correct motors for the doors and change one of the pigtails to match the motors. Oh the thrill of buying a truck all apart and not knowing what the heck was tampered with. Will update. Thanks for the help

Re: bench test pw motor
 

did some more research. Here's what I came up with. There is definitely a difference in the regulators between 78 and lets say 82 and up. Placed side by side they have slightly different curved bodies. (I believe this is because of the motor difference) Went to orilelys, auto zone and advanced. All three show two totally different motors to fit 78.
One is a flat bare metal one that I currently have and a black more of a box looking one.
Not sure how the silver would work with my harness (maybe they used both back then at different plants and would be different harnesses) as it is grounded through the switch which my harness does not have a ground as discussed earlier), I assume the black box one grounds through the door frame it is connected to. So I am pretty sure I need two new 78 regulators and two new black box motors. Will take a few weeks to get them off ebay as they are the only ones selling complete motors as the local parts house sell motors without the big gear device on the front. The pigtails are different also on these motors.

Re: bench test pw motor
 

seems like I am running into the same problem as my PW now with the door lock actuators . Put power to one side and ground the other and it works. Looks like reverse polarity as the window switches. It appears the po must have put all newer model stuff i the doors. Just call me Sean can you confirm as you did with the windows no revearse polarity on a 78. They are self grounding. Thanks

Re: bench test pw motor
 

anyone know where i can buy the correct self grounding door lock actuators? Ebay sells one that says fits all c10 73 up 88 But i know that cant be. Thanks

Re: bench test pw motor
 

looks like 1973-1978 are self grounding and in 1979 GM went to reverse polarity. According to LMC's parts catalog. And they sell only the 79 and up. Classic shows neither one.

Re: bench test pw motor
 

I wonder if you would have any luck buying a complete set of actuators, motors, switches and the related wiring (basically the door guts) from a forum member here on the parts board. Perhaps somebody is parting out a truck or has those sorts of parts laying around. A premium membership gives you the ability to post want-to-buy ads, and I have done that before with success for some parts, although not door parts.

Re: bench test pw motor
 

If I had to do over I would do just that. But now I am down the process to a point I cant turn back.

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Re: bench test pw motor
 

an update. Just got my door locks to work Yea. Got some correcting to do on this forum. First of all the actuators
i got to work iare the reverse polarity type (now not sure they make any other type). Although my switch has only three wires coming from it this relay has some sort of way of reversing polarity . I did not know I had (needed) until I found it in a box with the same color wiring on it as my power locks were in. So I connected it in line with what I thought was logical and wow it works. Now I am waiting on my new window motors to see if these old style motors need another one of these relays or I am correct they are self grounding. Thanks for everyone's help. It has been a struggle.