Relays for Dummies (2014)

So - one step forward- one backward. I installed my new switch and got the headlight and horn working perfectly. I thought that I would try the relays. I got the light relays in - high and low beam and they worked - for a minute or two. The main fuse blew; I think it was when I hit the horn. I wondered if I needed to put the relay on the horn so the switch was working consistently with horn and light; I have managed to have all circuits not work but still blow a fuse when I hit the horn. I powered the horn relay off the wire I connected to the main circuit that connects to the ammeter ( which came apart again - I have reinstalled the old one). I think that I have some bad connections in the ground wires- I have tried to join them altogether but the posi lock connectors are a bit bulky and cramped. Attached is a picture- despite my best efforts it is a bit of a dogs breakfast. I think I will just have to take everything apart and check it all, but is there any obvious fault or omission?

Chris T said:

So - one step forward- one backward. I installed my new switch and got the headlight and horn working perfectly. I thought that I would try the relays. I got the light relays in - high and low beam and they worked - for a minute or two. The main fuse blew; I think it was when I hit the horn. I wondered if I needed to put the relay on the horn so the switch was working consistently with horn and light; I have managed to have all circuits not work but still blow a fuse when I hit the horn. I powered the horn relay off the wire I connected to the main circuit that connects to the ammeter ( which came apart again - I have reinstalled the old one). I think that I have some bad connections in the ground wires- I have tried to join them altogether but the posi lock connectors are a bit bulky and cramped. Attached is a picture- despite my best efforts it is a bit of a dogs breakfast. I think I will just have to take everything apart and check it all, but is there any obvious fault or omission?

Click to expand...

Your discussion indicates either your wiring is correct, but fuse amp capacity is too low for simultaneous operation of lights and horn,

or,

there is a fault in horn or horn circuit.

Was horn blowing fuses before you made wiring changes? What is rating of fuse?

I would go back to wiring when everything worked, EXCEPT power horn relay thru a second fuse coming straight off battery. Then we can take it from there.

Slick

Blowing a fuse means you have shorted the circuit somehow. Basically you are bypassing an electrical load (i.e. horn, etc.) or a hot wire is going directly to ground. Poor ground connections do not make a short circuit. Double check the wiring to your horn relay.

Seeing how you are mounting the horn relay within the headlight shell, I drew a quick diagram showing the minimal amount of modifications that would need to be done to your existing wiring. Make sure you have wired your relay like this example. As you can see it looks different than the headlight wiring that I have previously shown. The numbers in parenthesis in the diagram are the numbers that are used on your relays. Pins #1 and #2 are interchangeable. Pins #5 and #3 are interchangeable as well. However I recommend wiring the way I show below so that you won't have to insulate the pin 87A from ground.



Basically you are only adding two wires to the existing motorcycle wiring. One wire would be from pin 30 (#3) on the relay to ground. The other wire would be from the ammeter to pin 85 (#1).

As you can see in the diagram when you press the horn button electrical current comes from the ammeter through the electromagnet within the relay to ground. The electromagnet then pulls the switch contacts number 30 and 87 closed. Thus completing the circuit for the horn.

Instead of hooking a wire to the ammeter, you could also tap into the headlight brown and white wire if you wish.

Normally you would mount a horn relay closer to the battery or the horn so that you would have the shortest possible distance for the power wire. I would wire the horn relay a little differently as well. But what I have shown here is the easiest way to do the job.
Pete

PeterJoe, thank you very much for your diagrams; they are very helpful. I have got the horn relay wired differently than what you show; so will have to redo that - once I work out the rest.

And Slick, I am using a 20 amp fuse. Any thoughts on that? That is the size fuse the bike has always had. As part of this process I also put a 20 amp fuse into wire that I am connecting to the main circuit at the ammeter, and off which I am powering the relays.

By way of further background I am running a prefocus halogen headlight bulb (and I have installed a Sparx three phase alternator and a Podtronics regulator - not that that should be relevant to this issue; not running at the time of testing). I use a Motobatt 9 ah battery, which I have hooked up to a multi phase charger, so it is fully juiced up when I am testing/using the circuit.

To my knowledge I have not previously had a problem of the fuse blowing when using horn with headlights, but that said I have had occasional blown fuses before with no obvious cause; I wonder if that could have been it. I have always had a problem with an unreliable horn; very sick sounding. I did replace the horn from stock with a cheap little one that I have mounted near the battery tray. The sick horn was temporarily fixed when I fitted the new switch at the weekend, it sounded good and reliable - after a few tries; but interestingly after I had ridden the bike to the testing station to get a new warrant of fitness (new switch fitted; no relays then), it sounded off. Luckily the tester was an old guy who tol me that he has a Triumph Speed Twin, and was sympathetic.

Incidentally I have just bought some new wire at the local Auto parts store (in this case Repco; the other main consumer based auto parts store over here is Supercheap - both Australian chains) so that I can redo the earth wires and make them tidier - by running them all outside the headlamp shell and then joining them and taking them to an earth point; as opposed to trying to connect them in the shell and taking up room that I don't have. The highest amp wire that they had on the shelf was 15 amp - which I bought - does this mean that if I am using a 20 amp fuse I am risking the wire failing somewhere on the circuit? Presumably the rest of the harness would not be rated any higher than this wire? And the wires in my new horn/dip switch are much thinner, and so presumably have a lower amp rating.

@Chris

Several points: ( no particular order)

1) a sick horn is indicative of a poor earth connection. test by running a temporary jumper wire straight to a good earth point, battery terminal is best. If jumper wire wakes up the horn, then probe for bad connections.

2) 20 amp fuses are fine in both your original circuit, and horn circuit. Wire rated for 15 amps will carry more than that if : current is not continuous as expected in a horn circuit, and wire is able to dissipate heat. The limitation to current is due to the insulation failing by heat, not by the copper conductor gauge.

3) install your horn fuse in the wire between the horn and battery (Peter Joe's diagram - wire NU). I would guess your horn pulls no more than 10 - 12 amps, thus a 15 amp fuse should be fine, but 20 is not excessive.

4) With a second fuse in the horn circuit, you should not blow either fuse unless there is a serious fault.

slick

I run 3 small modern type horns each one is rated at 1.5 amps they all are wired in parallel via a fused relay with 5amp rated fused (its loud) an horns hiden around the bike. I would think a 20 amp fuse for the horn is overkill.

Olds Horn can have a big absorption (Ampere) as my Austin Healey1957- Horns
https://picasaweb.google.com/lh/photo/v ... directlink
but if you aren't a Policeman - the use was so sporadic and short, that wire-harness-battery aren't stressed at all, also in our olds Commando-- so FUSE and RELAY are over shielded
Now also the Headlight RELAY MOD can be worthless, if use of a modern LED lamp is achieved
http://www.ebay.it/itm/8-16V-H4-High-Lo ... 2590bf4188

@all

Standard engineering practice to size a fuse is (US fuse mfgrs):

calculate: maximum amp draw x 1.25, then use fuse rated equal to calculation, or next higher standard rating, but not to exceed 1.75 x max amp draw.

No one has ever explained (at least I have not seen in print) what to do if no standard rating fits the calculation.....that's when you go on guts....

Slick

Bringing this back to the top because I need some help (apparently I don't fit the mold for "Relays for Dummies"). I got two 4 pin micro relays with diodes a couple years ago, just now putting them in for the headlight. Admittedly, I connected the relays incorrectly the first time, blew the main fuse immediately when I turned the key to lights and ignition. Ignition only is fine. Found PeterJoe's diagram here and wired correctly to his diagram, but still blow the main fuse when key is on. I'm wondering if I ruined the relays the first go around and now they're shorting out even though they're connected correctly now? PeterJoe mentioned if the relays have a diode, 85 and 86 must be connected correctly. I've tried swapping 85 and 86 and it still blows the main fuse. New relays required?
Everything worked as it should before I added the relays.

Brly said:

Admittedly, I connected the relays incorrectly the first time, blew the main fuse immediately when I turned the key to lights and ignition. Ignition only is fine.

Click to expand...

The relay diodes shorted from the reversed polarity. Oops.

Understood. New relays. I need to get another one for the horn anyway. Thanks!

I have sympathy for your challenges.

I attempted to fit relays to my bike for the horn and had all sorts of issues blowing fuses.

At the time I had change'd several components and modified the wiring and could not get the relay to work properly.

In the end the issue was an internal short to earth in a new regulator unit. It would work on the wooden bench but blew fuses as soon as it was bolted to the bike. But in the course of finding that I gave up on the relay because I was getting all sorts off contradictory tests on the multi meter.

So I guess my suggestion is to try and isolate one section at a time. And don't assume because something is new it is necessarily working

@Brly

You may (probably) have shorted the diodes the first time you incorrectly wired the relays in. Then, if shorted, wiring them correctly still results in a shorted relay. Only solution is new relays, wired in correctly.

A diode has a bar symbol at one end (ex. l---- ) the end with the bar MUST be connected to positive, otherwise you have a dead short.

You can test your diodes with a VOM set to Ohms scale. Connect the red lead to the bar end, the black to opposite, the reading should be infinity, then switch leads, the reading should be near zero. If you get the same reading both ways, the diode is shorted (near zero reading), or open circuited (infinity) and useless.

Slick

Just tested one of the relays, same reading either way. Toast.
Thanks for the help guys. I'll get some new relays.

texasSlick said:

Connect the red lead to the bar end, the black to opposite, the reading should be infinity, then switch leads, the reading should be near zero.

Click to expand...

You won't get infinity while the diode is across the relay coil - the highest reading you'll get is the coil resistance.

maylar said:

You won't get infinity while the diode is across the relay coil - the highest reading you'll get is the coil resistance.

Click to expand...

True .... my bad.

@Brly..... the test works if you disconnect one end of the diode from the coil.

Sorry to mislead.

Slick

Relays with diodes are used to protect very sensitive equipment, not sure if that really applies to these bikes. I run 5 relays, 2 headlight, 1 horn, 1 alarm and one for the Boyer MK IV ignition box. None of them have diodes. If I’m going to get a spike from a coil shutting off it will come from my starter relay.
If the diode did give up the ghost it probably failed as an open circuit anyway, so no current is going to flow through it. Depending on the relay you might be able to cut the diode out and use it as a standard relay. You can also source a similar diode and wire it in if you want to save that relay. Plenty of options available to you.
Pete

Deets55 said:

If the diode did give up the ghost it probably failed as an open circuit anyway, so no current is going to flow through it. Depending on the relay you might be able to cut the diode out and use it as a standard relay.

Click to expand...

Diodes can fail shorted also. Seems to be the case since the OP is still blowing fuses even with the terminals wired correctly. If the diode is internal to the relay it likely can't be replaced or cut out. Most automotive relays are sealed.

A relay is a device that controls a large amount of current with a small amount of current. You do not need a relay with a diode or any other "high" tech features for a motorcycle. As has been recommended the horn and the high and low beam elements of the headlight bulb should each have their own relay (total of 3). Add an additional relay for an alarm and possibly the brake light circuit especially if you have the non hydraulic Brembo brake light switch on your handlebar master; the one I'm about to mount has 22 ga. leads which are marginal at best for a 27 watt 1157 and inadequate for the wattage of the halogen counterpart. LEDs are game-changers for brake lights, but I'd still recommend a set of relays for LED headlights where each circuit is separately fused and NOT tied to the single harness fuse supplied from the factory.

I am a fan of the Centech AP-1 fuse panel:



This part insures that any one circuit won't shut down the motorcycle, unless, of course, your ignition circuit is the culprit. I fuse the headlight beams, the ignition and the horn separately which leaves me an extra fused circuit for my microwave oven or my TV...

Best

Agree with Deets55 Reply #37..... most relays for automotive use do not include diodes. No harm will come from using without, except perhaps an insignificantly shorter relay life.

Also agree with maylar, Reply #38.

Slick