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  #1  
Old 07-14-2018, 08:47 PM
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76 280c power to relay test

Does anyone know how to test for power in a window relay box ? For a 76 280c 114073 coupe.
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  #3  
Old 07-15-2018, 12:31 PM
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76 280c elay test

Quote:
Originally Posted by Diseasel300 View Post
Other threads you've started on this same subject:

http://www.peachparts.com/shopforum/vintage-mercedes/394174-76-280c-114073-chassis-no-power-windows.html
http://www.peachparts.com/shopforum/vintage-mercedes/393923-76-280c-power-window-regulater.html
http://www.peachparts.com/shopforum/vintage-mercedes/393876-multi-meter-reading-power-window-switch.html
http://www.peachparts.com/shopforum/vintage-mercedes/393858-76-mercedes-280c-power-window-switch-wiring.html
http://www.peachparts.com/shopforum/vintage-mercedes/393789-76-mercedes-280c-chassis-ground-locatations.html
http://www.peachparts.com/shopforum/vintage-mercedes/393670-76-280c-power-windows-no-power.html
http://www.peachparts.com/shopforum/vintage-mercedes/393329-1976-280c-no-power-powerwindows.html

Pick a thread, stay with it until you've solved the problem. Starting a new thread every couple days is going to get you nowhere fast.
looked at all the threads . still no answers how to test for power at relay . my problem is no power to switches . fuse box cleaned and new brass 16 amps. only see power at 30 on relay . with key on no power to other terminals .
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  #4  
Old 07-15-2018, 01:25 PM
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The reason you have no answers is because you've been told the answer several times in various other threads. Get the FSM, get the wiring diagram, and troubleshoot. Nobody can snap their fingers and give you a magic answer, the only way you're going to find the issue is to start at the source, take a multimeter and start tracing the circuit. If that isn't something you can do yourself, find an automotive electrician and have him trace the circuits to find the fault.
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Old 07-15-2018, 06:07 PM
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Quote:
Originally Posted by Diseasel300 View Post
The reason you have no answers is because you've been told the answer several times in various other threads. Get the FSM, get the wiring diagram, and troubleshoot. Nobody can snap their fingers and give you a magic answer, the only way you're going to find the issue is to start at the source, take a multimeter and start tracing the circuit. If that isn't something you can do yourself, find an automotive electrician and have him trace the circuits to find the fault.
ok one question whats fsm mean ?
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  #6  
Old 07-15-2018, 06:48 PM
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FSM = Factory Service Manual.
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  #7  
Old 07-16-2018, 08:39 PM
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Testing one of the four prong relays is easy. First you pull the plug on the relay and find out if you have power to the relay.

Just ground out the negative probe of your voltmeter and then poke the positive probe into the socket holes. One at a time.

Oh, yeah, set your voltmeter to the 20v dc setting, or in that range depending on what your meter has for settings.

Turn on the key to power up the system. Out of the four holes in the socket one of them should test at least 12v dc.

So now you have power to the relay.

Next remove the relay from the car. Our of those four prongs one is positive, one is negative, and two are volts in and volts out.

You know which is the 12v positive pole. You just found it on the socket. So line that up with the prongs on the relay and hit it with 12v positive. (Run a wire over there from your positive terminal of the battery) One of the poles next to it is the ground. So run a wire from the body of the car or the engine block to the relay pole next to the 12v + and you should hear a click. If no click touch the other pole. You should hear a distinct click. If you are holding the relay in your hand you will also be able to feel it.

So now you have established the 12v + pole and the negative pole. Hook them up and after the relay has clicked (also known as 'pulling in') check for continuity across the two remaining poles. You should have continuity.

If there is no click the relay is bad. If there is a click and no continuity the relay is bad.

These can be redone if you carefully pry off the cover of the relay and clean the contacts on the relay. This would only fix the no click condition and maybe not even then.

If the relay is bad then start searching for another one. BE WARNED: These are not cheap. A tested used one might be a good way to go if you have to replace it.

And you should have about three of these relays on your car. Swap out a relay from another position and see if your windows work. Once you discover a bad relay then you need to find if this is your only problem. Swapping out relays on your own car is a fast way to find this out.
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  #8  
Old 07-20-2018, 11:05 PM
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Quote:
Originally Posted by Idle View Post
Testing one of the four prong relays is easy. First you pull the plug on the relay and find out if you have power to the relay.

Just ground out the negative probe of your voltmeter and then poke the positive probe into the socket holes. One at a time.

Oh, yeah, set your voltmeter to the 20v dc setting, or in that range depending on what your meter has for settings.

Turn on the key to power up the system. Out of the four holes in the socket one of them should test at least 12v dc.

So now you have power to the relay.

Next remove the relay from the car. Our of those four prongs one is positive, one is negative, and two are volts in and volts out.

You know which is the 12v positive pole. You just found it on the socket. So line that up with the prongs on the relay and hit it with 12v positive. (Run a wire over there from your positive terminal of the battery) One of the poles next to it is the ground. So run a wire from the body of the car or the engine block to the relay pole next to the 12v + and you should hear a click. If no click touch the other pole. You should hear a distinct click. If you are holding the relay in your hand you will also be able to feel it.

So now you have established the 12v + pole and the negative pole. Hook them up and after the relay has clicked (also known as 'pulling in') check for continuity across the two remaining poles. You should have continuity.

If there is no click the relay is bad. If there is a click and no continuity the relay is bad.

These can be redone if you carefully pry off the cover of the relay and clean the contacts on the relay. This would only fix the no click condition and maybe not even then.

If the relay is bad then start searching for another one. BE WARNED: These are not cheap. A tested used one might be a good way to go if you have to replace it.

And you should have about three of these relays on your car. Swap out a relay from another position and see if your windows work. Once you discover a bad relay then you need to find if this is your only problem. Swapping out relays on your own car is a fast way to find this out.
THANK YOU VERY MUCH GREAT ANSWER I GET POWER TO PIN 30 ON BATT BUS KEY OFF WITH KEY ON 1 OR 2 POSITION I GET NO POWER TO 86 OR GROND PIN THINK IM IN FOR SERIOUS WIRING DIAGNOSTIC TRYING TO FIND THE GROUND LOCATIONS NO LUCK YET
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Old 07-21-2018, 07:26 PM
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Quote:
Originally Posted by huffandpuff View Post
THANK YOU VERY MUCH GREAT ANSWER I GET POWER TO PIN 30 ON BATT BUS KEY OFF WITH KEY ON 1 OR 2 POSITION I GET NO POWER TO 86 OR GROND PIN THINK IM IN FOR SERIOUS WIRING DIAGNOSTIC TRYING TO FIND THE GROUND LOCATIONS NO LUCK YET
You have located the 12v +. That is a good first step. The ground will be the pin next to it.

Put your tester on ohms. Touch the leads together and your needle should jump or if digital your meter slould read zero. Then you know your meter is working.

Find an unpainted spot on the car to touch one lead to. Any place on your engine block will do, or if your leads will reach touch one to the negative battery pole. Then touch the holes in the socket. One of the pins next to the 12 v + will be the ground.

If there is no ground you have found a problem. You may be fighting several problems. This grounding thing need to be corrected before you can continue testing the system.

I don't remember if there is a central grounding point or not. I know some Merceds of that vintage have a central grounding point in the trunk area, on the left hand side of the car. A lot of brown wires will come together and be screwed to the floor. But this might not be the case with your car.

The ground wire will be brown. During those years all ground wires were solid brown.

It is not a bad policy to unscrew the screw that screws the grounding wires to the body every few years and clean the wires and the body area where they screw down. Resistance can build up this area, too, and drive you crazy when trying to run down an electrical problem.

Another tip that has nothing to do with this relay: Replace the grounding strap that runs from the engine to the frame or body of the car. These break down inside and will resist current flow. This drives your ignition system nuts and will give you all sorts of weird idle problems.
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