Testing relay boards...., Can you bench test a 914 relay board....??? Options

[second wind]

Hello out there....my car has been dying after getting a good warm up but starts the next morning. The tell tale symptom is that the fuel pump does not run when the stall occurs and even after hours of cooling off it still does not start...but it does in the morning....???
So talk on the street is the relay board is too old to work properly.....the description of 914 LTD's improved and rebuilt relay boards matches the symptoms of my car perfectly so as soon as I scrap up the money I will buy one.....meanwhile I have two spare relay boards and one looks really good. Is there a way to bench test the relay board before I swap the boards ?? These cars sure keep you on your toes and a relay board with fresh soldered connections sure sounds appealing so Brad is holding one for me. So back to the swap out....I hate to go to the effort just to install another faulty board. Look forward and appreciate any and all comments and help....thank you very much!!!!
gg

[dr914@autoatlanta.com]

Here is an old guy explaining the function

https://www.youtube.com/watch?v=YLgQxpNHzIU

[second wind]

Here is an old guy explaining the function

https://www.youtube.com/watch?v=YLgQxpNHzIU

Thank you very much George...great video! At the end I thought you were going to show us how to test a relay....is there a procedure for this? I have some of the new 914 Rubber relays....they usually make quality parts....have you had any experience with those? Thank you again,
gg

[Superhawk996]

At the end I thought you were going to show us how to test a relay....is there a procedure for this?

Take a look at the SirAndy board graphic on page 1 of this thread.


The schematic for the relay is shown.

Pins 85 & 86 are the solenoid coil. I have a good one in my hands it reads 69.7 ohms and draws .15A when connected to my power supply @ 13.6v

Pin 30 is the uncontrolled side of the relay. It is where the circuit to be controlled (usually 12v power) is usually fed into the relay.

Pin 87a is the normally closed contact. It is connected to pin 30 when the solenoid is not powered.
(this should read 0 between pin 30 and pin 87a ohm when the solenoid is not powered

Pin 87 is the normally open contact
(this should read infinity between pin 30 and 87 when the solenoid is not powered)

When the solenoid is activated by applying 12v power across pins 85 & 86, the resistance between pin 30 and pin 87 should change from open (infinity) to zero ohms. it doesn't matter what polarity goes to which solenoid pins - a solenoid doesn't care, it's just there to act as an elecromagnet.

The pins are clearly marked on the old German relays.


The solenoid can be bench tested with a couple test leads and a 12v battery connected across pins 85 & 86 while looking for the resistance changes noted above.
@second wind

I just tested 3 that came off my old relay board. 2 not working. Moral of the story - bench test to know you're dealing with a good relay. And don't ASSUME that if it works cold that it will work when hot. There are electrical connections and moving parts in the relay that may change behavior or become intermittent with temperature. They shouldn't - but they can.

This sort of testing is why a DMM is CRITICAL in my opinion. You could rig up the same bench test to work with a simple lighted test probe, but it's more work. Yes, you could see if the relay is working, but you can't measure resistance with a simple test light.