Test dimmer relay

I'm assuming this is a US car.

This page of my web site:

for: " Headlight dimmer relay circuit '71 thru '79." Apply 12V between #56 and "S" terminals and relay should click. (If it clicks when you pull the lever, disregard this test.)

If it clicks but is stuck on Low beam, then the relay is bad.

The fuse block relay terminals are proprietary and I doubt you could find them anywhere in quantities less than 1,000. If the splice works, leave it alone.

Speedy Jim

"I have no use for a car which has more spark plugs than a cow has teats!" Henry Ford, when advised that Chevrolet was introducing a 6-cylinder engine.

Well, it looks like the relay is bad.

Thanks for the diagram Jim. It was helpful in troubleshooting the problem.

I confirmed that terminal #30 had 12v(+) all the time. Terminal #56 had 12v(+) when the headlight switch and ignition switch were both on. One of the two terminals #56a or #56b also had 12v(+) whenever #56 had power (can't recall which, but it was powering the low beams). I tried grounding the "S" terminal manually, but nothing happened. No click, no change at terminal #56a or #56b. Bad sign for the relay. I also confirmed that terminal "S" was grounding each time I pulled the turn signal level (dimmer switch).

All of this in the dark w/ a flashlight while it was raining lightly. With a circuit tester and a few jumper wires... no fun :-(

I guess electrical components don't last forever. I've already mail ordered a new relay (as well as a few extra parts :-)

Thanks Jim for the help.

AshMan40

Okay, now I'm a little upset (just a little).

My new Dimmer Relay lasted a whole day before it too stopped working. Unlike my original relay, it got stuck in the High Beam position. Can't be driving around at night w/ my "brights on" so I swapped my old relay back in and broke open the new relay too see what was going on.

Inside, I see some fancy levers and contacts. There is a plunger and a see-saw like lever that switches between the high/low contact. I can see the coil, a diode and an exploded resistor! The resistor is wired near the top of the relay and could easily be de-soldered and replaced. The problem is, since it looks like it exploded, there's no way to identify the colored stripes! The area where the stripes would be is where it looks like it exploded.

Anyone have any ideas on what rated resistor should be installed here?

I believe you can make out the relay schematic from the diagram stamped on the outside of the relay casing:

'','width=350,height=400,toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes' Also, has anyone had a relay go bad on them so quickly? I'm considering spending twice as much to get a German made one from my FLOPS.

AshMan40

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Try something around 200 Ohms, 1 watt rating. It should not be a critical part.

Usually the relay fails due to overheating of the contacts (from the Amp load) which distorts the plastic bits.

Speedy Jim

Well, I tore into my dimmer relay today. The resistor that I thought was blown seems okay. My multimeter reads 98ohms of resistance in either direction. So it's still good and not a diode like I suspected it might be. FYI - The function of the resistor/diode in the circuit is to reduce the arcing at the relay contacts due to the high voltage inductive discharge from the coil that can come from quickly switching off the relay (coil). It gives the charge someplace to go instead of arcing across the contacts and possibly welding the contact together. A resistor is the cheapest solution, but diodes are better and more common (according to many websites I came across).

The bad thing... there is no continuity thru the my relay's coil. The relay is shot :-( I was able to take some photos of the inner workings of the relay so that anyone else might be able to troubleshoot their future problems. The mechanism is quite interesting and useful if you are looking for a bi-stable (can rest in both states) latching relay.

Here are the pics:

I've order a used (German) relay from one of the Samba classifieds. Hopefully it will be more reliable. Otherwise I'm building myself my own relay from common Bosch 30A SPDT relays! KISS

AshMan40