How to test the horn relay?

[John_Mc]

Guys, I have an intermittent horn issue and I suspect the relay, although I’ve taken the relay off the car and bench tested it and it works!  Yes I know the wiring looks horrible and so I have completely replaced the ground lead from the horn switch to the relay and I have continuity.  Is there a foolproof method to test this original relay?  Here is what I have at the moment.  Thanks in advance.

 

 

Edited March 28, 2019 by John_Mc (see edit history)

[19tom40]

John, the relay is probably  OK, it sounds like the contact points are dirty. You should be able to carefully pry off the cover and  clean the contacts. The contacts are probably silver and very soft, so do not be aggressive in cleaning. Some relays had contacts that were silver plated and those will corrode very quickly if cleaned with an abrasive. I like to just soak a piece of cardboard like a matchbook cover with contact cleaner and rub that across the contacts. If they are pitted   you can use     wet or dry  600 paper to clean them.

 

After cleaning the contacts, operate the relay by hand and observe the fixed contact. It should move about .010" when the relay armature is fully activated. It can be bent to achieve that wiping action.

[John_Mc]

Thanks Tom, I’ve already done as you had written last year, but I’m wondering if over the winter if the points corroded OR if i was too aggressive in cleaning the points.  It must be the relay however because should I bypass it, the horns do blow.  Thanks as always for your insight.

[19tom40]

John,

 

When you press the horn button it completes the circuit to pick the relay. The 6 volts from the battery then goes through the points to the horns and operates the horn motors.

 

If you have the relay back in the car, try this:

Plug you ears and put on ear muffs.

Connect your volt meter COM or black lead to the NEG post of the battery

Connect the + or red lead of the voltmeter to the wire that goes to the horn motor

Press the horn button or use a jumper to ground the wire from the button

Read the voltmeter with the horn operating. The reading should be 0.2volts or less. This reading is the voltage loss due to resistance in the horn circuit.

If the reading is higher than 0.2 volts, move your lead back to the input of the relay and repeat the test.

If you still have a high reading, check all of the connections from the battery to the horn relay. If it is normal, clean the relay contacts.

If the reading is 0.2 volts or less, check the ground circuit by connecting the red lead of your meter to the POS terminal of the battery and the black lead of the meter to the horn mounting. This reading should be 0.1 volts or less. If it is greater than 0.1 volts then you have a grounding problem.

 

If the readings are within specs, the problem is in the horn motor, try cleaning the horn motor contacts.

 

Unplug your ears, so I don't have to shout at you on April 6th.

 

 

[John_Mc]

Thanks again Tom for the input.  I found my problem.  It is a sticking relay.  I was frustrated because it would work sporadically.  Then after checking all the connections I tapped the relay with a hammer............the horn has worked perfectly ever since!  

[John_Mc]

11 hours ago, 19tom40 said:

John,

 

When you press the horn button it completes the circuit to pick the relay. The 6 volts from the battery then goes through the points to the horns and operates the horn motors.

 

If you have the relay back in the car, try this:

Plug you ears and put on ear muffs.

Connect your volt meter COM or black lead to the NEG post of the battery

Connect the + or red lead of the voltmeter to the wire that goes to the horn motor

Press the horn button or use a jumper to ground the wire from the button

Read the voltmeter with the horn operating. The reading should be 0.2volts or less. This reading is the voltage loss due to resistance in the horn circuit.

If the reading is higher than 0.2 volts, move your lead back to the input of the relay and repeat the test.

If you still have a high reading, check all of the connections from the battery to the horn relay. If it is normal, clean the relay contacts.

If the reading is 0.2 volts or less, check the ground circuit by connecting the red lead of your meter to the POS terminal of the battery and the black lead of the meter to the horn mounting. This reading should be 0.1 volts or less. If it is greater than 0.1 volts then you have a grounding problem.

 

If the readings are within specs, the problem is in the horn motor, try cleaning the horn motor contacts.

 

Unplug your ears, so I don't have to shout at you on April 6th.

 

 

My wife claims she has to yell at me all the time.  She says its my hearing..........but i think she just enjoys shouting! 🙂

[19tom40]

John, what size hammer is used for this fix?

 

You might want to remove the cover and put a drop of light oil on the pivot points to prevent further sticking.

[John_Mc]

6 hours ago, 19tom40 said:

John, what size hammer is used for this fix?

 

You might want to remove the cover and put a drop of light oil on the pivot points to prevent further sticking.

Tom, never thought of that, but what type of oil?  Light machine??

[19tom40]

3 in One or a similar oil. You just want to flush the dirt out and leave a light film of lubrication.