How do I know if a relay is bad?

[Rich 89 Gr. Wag]

OK, I pulled the rear window defogger relay out of my 89GW, reinstalled fuse #4, and the battery drain is gone. Everything works fine with the obvious exception of the defogger. The silver module is 1 1/2 x 2" and has 4 prongs for two connectors/plugs. There are 3 prongs for one plug and are labelled L, P, and B. The is one prong labelled G, and there was nothing plugged to that prong when I opened the access cover.

I have a multimeter, but am not sure what results to look for. Anyway, here are the results on the multimeter. Does anyone know how to read them? With the positive probe on the first prong and the negative probe on second prong I get the follwing movement on the meter:

LP, big jump
LB, no movement
LG, big jump
PL, big jump
PB, no movement
PG, moderate jump
BL, moderate jump
BP, small jump
BG, big jump
GL, big jump
GP, small jump
GB, no movement

I'm guessing that L means lock (for tailgate), P means power, G means ground, and B - I'm not sure. Thanks in advance.

Rich

[cantdrive55]

hmm, all of those pins and relay specifics mean nothing to me but here is how you check a relay.

There should be 4 pins, 2 pins are the control circuit. The other 2 pins carry the bigger current. Rather than running the high amount of voltage it takes to move a window through a big switch the control circuit uses a little voltage to close a contact in the relay. Those closed contacts in the relay carry the heavier current.

Hope that makes sense but no matter. All you need to do is use a jumper wire to battery power to one of your contacts and ground another contact. Try different combinations until you hear a click. The click means you have closed the internal contact. When that happens use your meter and check for continuity across the other two contacts. You should have 0 ohms of resistance.

If no combination will make your relay close, it's bad. If your relay closes and you don't have continuity across the other two left over contacts, it's bad. If you remove power from your relay and you still have continuity (0 ohms) across your other two contacts, it's bad.

Hope that makes sense. Good luck.

[jeepbob]

His problem seems to be a fused relay. The contacts are prolly welded together. Rich, it sound like you have found your problem either replace the relay or take it apart to satisfy your curosity and replace it anyway. :D My manuals are not new enough to be of help with the relay term ID.