Originally Posted by NDavies4

I have an intermittent rough idle + occasional stall problem on my '92 300 CE-24 cab that I've been told many times is probably the OVP relay, but as it was replaced only 2 years ago I kept ignoring the advice.... til last week that is:

Read an article in a MBZ Club magazine here in the UK that described how to test the relay. It states:

"Test 1: Connect pin 30 to a +ve 12v supply and pin 31 to the -ve. Under this condition the only output should be on pin 30a.

Test 2: Now connect pin 15 to the +ve and both relays should operate with supply voltage appearing on both pin 87E and 87L".

When I did these test on my current relay, Test 1 was fine but Test 2 gave no reading on 87E or 87L, which I took to indicate that the relay was dead. I therefore ordered a new one which I got at the weekend and tested today. I was amazed though to get identical results - i.e. +ve on 15 and -ve on 31 still gave no reading off either 87E or 87L!!

Does anyone know if this test is valid and I'm doing it correctly, or is it simply that both the current and the new relay are duff and by some coincidence failing in an identical way? Also are there any other tests that can be done on the relay to test its integrity?

Note, both relays are #201 540 37 45 (9 pin, 2 red fuses and made in Hungary).

Regards,
Neil