The Stovebolt Site Forums The Shop Area The Electrical Bay Problem bench testing horn relay

I do not understand everything I know about relays. I decided to use a horn relay on my 1952 3100 even though it did not come with one. I am using the original horn but converted to 12 volts and am worried about frying the little contact spring in the horn button.

I wanted to verify the aftermarket 12v relay worked (as described in many posts) before I wired it into my new wiring loom. There must be something flawed in my testing logic because it doesn't seem to be working right. I am using a motorcycle battery and with the positive lead hooked to any of the three terminals the other two terminals will light my test light with the other end connected to the negative battery terminal. Depending on how it is hooked up you also get a click from the relay when the test light is attached. It does not seem to matter if the body of the relay is grounded or not- still get the test light coming on the 2 terminals not connected to power.

My understanding was the relay would not connect the 2 feed terminals unless the 3rd terminal was grounded. This does not seem to be the case with my relay or the way I am trying to test it just isn't correct.

Any advice is much appreciated.

Chuck

Chuck,when I go out to the truck latter I'll look at the relay and post how it's wired.


Pete

Don't know bout the aftermarket relays but here is the stock relay for the '54.
http://www.pbase.com/dennygraham/image/137465846/large
Denny Graham
Sandwich, IL

Thanks for the help so far guys. I understand how it is supposed to be wired- there are plenty of posts describing this. My issue was I wanted to verify the relay worked as I understood before I cut into my new wiring harness and wired it in.

So do I have a bad relay?
Is my testing method flawed?
Can I fry the relay if if power was supplied to the wrong terminal?

Chuck

The basic idea behind the horn relay is power is always applied to the relay coil and to one side of the NO switch. When the horn button is pressed, this grounds the relay coil which in turn pulls the relay wiper and connects the two relay poles (causing the click noise). The power to the horn does not pass through horn button. It is direct from the source through the relay contacts to the horn itself, then to ground.

If you would like a diagram I can draw one up.

Dale

In Denny's photo, it appears the black (top wire) goes to the horn, the red (middle wire) is the power source and the smaller natural color (bottom wire) is the coil ground back to the horn button.

Dale

here is the diagram that came with my after market horn relay i got from my local auto parts store.

...pic...

from the description of your test it sounds like you have a bad relay.

on your bench test with power to the center post you should only read power on one other post.

Also, if you apply voltage to the horn terminal, you should see nothing on the other 2 terminals. Kinda sounds like the relay contacts are "welded" together.

Hmmm
No drawing no photograph. Can you send a crystal ball?

Dan Bentler

Dads50 and wald53 thanks for confirming what I suspected. I was a little hesitant to condemn it because I just don't understand the internal workings and I was really only testing it to confirm it was wired like all the other posts have described (and Denny's is wired). My relay came with no instructions at all. It did have a label stating made in USA in English, Spanish, and French. That is a refreshing change but a bummer it is a bad part. It has the same exact numbering system on the back as the sheet waldo53 has posted.
It certainly doesn't appear to be working as it should but it still clicks so I am not sure anything is stuck inside.
I am just going to try another one. Thanks for all of the advice.

Chuck

Your testing method is flawed. You shouldn't be using the test light as your ground.

Using the diagram Dads50 posted, connect a jumper wire from the positive of the battery to the center post of the relay. (battery terminal) Use another jumper with your test light from battery - to the 'horn' terminal. This is easier if you have jumpers with clips. Now connect another jumper to battery -. When this last jumper is touched to the 'switch' terminal it should ground the coil, causing the click. This will apply power to the horn terminal and your test lamp will light.

Thank you very much Cletis. Saved me again.

Chuck