This one is driving me nuts. . .

I have a 12V air compressor and horn. When I hook it directly to the
battery, I get a nice loud BCD awakening blast.

I hook it to a relay and get nothing. When I push the horn button,
I hear the relay click, and read 12V coming from the relay.
But the air compressor shows no sign of life.

Thinking perhaps it cannot draw enough current to run the compressor,
I hooked up the stock electrical horn to the relay instead. Still nothing.

I tried measuring amperage and get 0 when holding the button, and
a brief spurt of something when I release. Is that because the
multimeter itself has no draw? Not sure how I'm supposed to use the
amp meter functionality.

So my multimeter reads 12 VDC and 0 ADC when I push the
horn button.

I have tried 3 different relays. I am using ones labeled "12V 20/30A".
Is that enough? (What's with 20/30?) Maybe I'm frying the relays?
Maybe I'm just an idiot?

I'm going to try one more thing now: a Mich Ultra.

Ted

K, keep in mind what a relay is and does. Essentially you have two leads that power the coil (magnet), this is what you hook to the battery and your horn switch. Then on the other side, you have two more leads. You ground out your compressor, run a power line from a fused power source, to the connection on the relay. Then a wire from the last free connection out to your compressor. So when the power is applied to the coil, the magnet will draw a metal plate to connect the other two leads completing the curcuit between your powersource and your horn.


Does this make any sense? I can draw it out if you want.

Yes, I'm pretty sure I understand how it's suppose to work.

These are my connections:

1. Positive battery terminal to inline 30A fuse to terminal "30" on relay.
2. Existing 2 horn wires to terminals 85 and 86 on relay. I assume
it doesn't matter which way.
3. "87" terminal on relay to positive terminal on air compressor.
4. Negative terminal on compressor to bike frame.

When I push my horn button, I hear the relay click and am
measuring 12V from the wires going to/from the compressor.
The fuse between the battery and relay is not blowing.

Ted

Huh? I just changed connection #4 above to go
directly to the negative battery terminal - and it works!

But if my ground connection was no good, why was a
getting voltage reading??

Thanks for the help.

Ted

When you were checking voltage were you checking the negative at the point where you grounded it, or to the battery? It sounds like the relay was allowing the 12v to get to the compressor, but with the bad ground there was no completion of the circuit. Floating 12v. Remember too that your volt meter doesn't measure voltage, it measures the difference in voltage between the two leads.

Gotta love voltage drop :]

Hmmm - - I might have been checking the voltage between
relay terminals 30 and 87 - - which would not have accounted
for a bad ground to the compressor.

Anyway, I'm ready to go hunting for sleeping cagers now. :grin:

Damn - - upstaged already! There is a fire station across the
street from me. I want one of those horns!

Your 30 amp relay wouldn't work for THAT horn.

I always wanted a train horn. :bigshock: