Headlamp Relay Replacement - AutoZone #16227 $7.99

[kboehringer]

XS Folks,
I'm doing some last minute fixes and found a replacement for the often faulty 35 year old OMRON headlamp relay.

With the help of my Master Electrician at work, we found this relay offered at Autozone he felt would work:

http://www.autozone.com/electrical-a...se/679356_0_0/

It's 12volt and rated for 20amps.



Very easy install requiring no re-wiring. I pulled the stock female connectors from the OEM 4-way plug and put them directly onto this relay with a little heat-shrink around each. The relay is a bit smaller than the OMRON.

Just checked and it works great for a mere $8.

KURT

[TopCatGr58]

Hey Kurt,

Well, you're lucky that it works, and here's why. The OEM headlight relay is not just a standard relay. It's a LATCHING relay, it stays thrown until the power is removed from the switch side. The relay switch/throwing circuit is powered/triggered by the ALT sending power to it once the engine is running and the ALT is providing charging current. Each leg/phase of the ALT provides about 7 volts AC, and is then simply changed to DC with the use of a diode in the line to the relay. That's the white wire to the relay. It's designed to NOT draw much power from that phase tap line....just when the relay is first thrown...then it's NOT supposed to keep drawing power...it just stays latched without drawing power.

However, your relay requires +voltage to keep it thrown/engaged all of the time.....so it's drawing power from that one leg/phase of the ALT circuit. Now, how much, I don't know...so don't know how much of an impact in the overall wattage production of the ALT due to any loss of voltage from that leg powering the headlight relay?

My relay quit working because my trigger wire from the ALT quit providing the power...I think because of the diode burning up. I replaced the diode, but it still didn't work. The relay still worked though. So...I setup a separate switch and wire to feed the relay that I could throw once I started the bike. I throw the switch and then unthrow it so that it doesn't keep sending power to the relay. IT stays latched, and my headlight stays on until I turn the bike off again.

T.C.

[bikerphil]

TC, on the 80-81 bikes, isn't the latching diode in the wiring harness? The early relays had the diode inside them.

[TopCatGr58]

Yes, and I found it, replaced it and still didn't work? By this time I had put on my auto race alt, but had wired up a phase tap on it like the OEM because I had found that it had the same hertz for the Tach. I wired in a Y and ran one to the White relay wire, and 1 to the other white wire for the Tach. My tach did work, and still worked even when the relay stopped responding?? I eventually replaced my gauge cluster with the new electronic one, using a wire off of one of my ignition coils for the tach trigger, and as stated, I had already wired in my separate switch to throw the headlight relay using regular 12+ power, but can switch it back OFF so it doesn't keep the relay energized/drawing power.

T.C.

[kboehringer]

Hey Kurt,

Well, you're lucky that it works, and here's why. .................T.C.

TC
Well, I'm staying with the AZone relay and not adding another switch. I also replaced the Diode with one from Radio Shack. Works fine for me......

Kurt

[CaptonZap]

Actually, you can make a latching relay out of that by putting a diode in the circuit between terminal 5 and 1. Make the band on the diode connect to the 1 terminal. and the other end to the 5 terminal. The diode isn't going to carry more current than the coil draws, so it doesn't have to be very big.

CZ

[MPittma100]

Relay

I tried a relay of this type with no wiring mods on a 1979SF. It worked for a while, then failed. Bought a used Yamaha relay off eBay. It has worked for several years now.

[skids]

The good thing about the 78 and 79's is you have an on/off switch at the left handgrip. You don't have to use the signal from the alternator. I really like the ability to switch off the headlight.

[BA80]

Deleted my relay with 2" of wire and 2 spades. Headlight just comes on with the ignition.

No more relay or diode worries.

[natemoen]

The good thing about the 78 and 79's is you have an on/off switch at the left handgrip. You don't have to use the signal from the alternator. I really like the ability to switch off the headlight.

Only the '78'S had the on off switch.

[ViperRon]

You may find the relay works but as TC said it is actually receiving pulsed DC and this tends to heat components it may work well for a long time but I'd have a plan for that cold night ride when it quits.

[CaptonZap]

You may find the relay works but as TC said it is actually receiving pulsed DC and this tends to heat components it may work well for a long time but I'd have a plan for that cold night ride when it quits.

Actually, if you trace the circuit, you find that once the relay is latched in, the current holding it in is battery voltage, i.e. DC. Any over voltage pulses from the white wire would be absorbed by the battery, and since the regulator is controlling the output of the alternator at that point, the voltage spikes would probably be no more than a fraction of a volt, and thus the equivalent of some DC ripple, which won't hurt a quality relay coil.
In defense of after market relays, not all of them are built to a "gold" standard, and the failure rate of one brand can be many times higher than another. Since we don't know what brand it was, and what caused the failure, it would be foolish to brand them all as bad choices. The ratings on the relay should be checked against the usage that you intend to put them to.
"95% of functional deficiencies are due to operator error". Anon.

CZ