How do you test a relay?

[TCMdocs944]

Any idea?

[Chris_924s]

I usually swap it out with a known good one from another 944.

Relay contacts should be clean and free of oxidation. In the "old days" we would remove the relay cover and apply proper voltage to see if the contact moved.
WITHOUT VOLTAGE APPLIED- To check the resistance you can use the "Old paper trick" to manually close the contact, and use an ohmmeter on the pins to check throughput of the closed contact to see if it's ok.

[Texas944]

which relay are you wanting to check?

[TCMdocs944]

Theoretical question for the moment.


I am going over every inch of this car in the 'bring it back to life' process. I want to rule out all electrical problems (and vacuum) before I dig deeper on some of my drivability issues.

I want to pull each relay..one at a time...clean, test and replace it.

I was hoping for a voltage to the pins and listen for the click type test.

Are the individual relays actually that different?

[Texas944]

i think most of the relays are regular style ones, but the dme relay is actually 2 relays in one - so in order to test it correctly, you would have to energize both relay coils. At the same time you would also have to check for continuity across the contacts with a meter. Cant you rule out if a relay is working correctly by whether or not what it controls is getting power? ie:A/C clutch is working so therefore the A/C relay must be too?

[TCMdocs944]

That kinda makes sense but.....


for instance.

My intermittent wipers do not work..they have a relay...I am wondering what else is not working properly because of this...

Yes. It should only be the wipers BUT... as we all know, with this car that doesn't really mean anything.


Would be much easier just to pop it out and test it if there was a way or a little box you could plug it into.

[Texas944]

aint that the truth!

do you have the schematic from the porsche tech cd so that you can chase and check wires?

[Paul Glasson]

Most relays have a diagram showing pin configuration.Remove relay. You should take 2 crocadile clips (leads with spring loaded clips either end) connect one lead to positive and one lead to neg of battery and the other ends can then be connected to the 2 coil pins on the relay. The n/o and n/c contacts can each be tested in turn using a multimeter holding meter leads with similar crocadile leads to contacts being tested. Energise and deenergise the coil by connecting and disconnecting one crocodile lead from battery. The normally closed contact reading should change from a few ohms to infinity when energised & vica versa for n/o contacts.
It is easy to plug the relay back into the wrong base pins so beware they go back to the same place.

[epbrown]

There's a write-up on relays in the latest 911 & Porsche World that talks about testing and how/why they fail. Worth a read if you've got a Borders or B&N nearby.

Emanuel