Technical Headlight relay question

If 85 & 86 are good, you could jump from 30 to 86 and see if the lights turn on. If they do, the relay is good and you'll need to check your signal wire that goes to 86.

 

85 & 86 are the switching points, one side ground, the other from headlight switch,
30 is fused battery
87 goes to head lights,
87a is live till the relay switches to 87

Be sure battery voltage is at 30 terminal & 87a
Be sure you have voltage at 86 when headlight switch is on
Be sure you have a good ground to the relay
ARE YOU SURE you are on low side output of the dimmer switch? or bright side if relay is for high only.

 

so wait, is 87a supposed to be connected? I thought 87 a is unused

 

Use a test light and check the 86 tab to make sure you have power from the headlight switch. Then, check 87 with the switch on to see if you have power, if it has power check the headlight (for ground and power). If you have no power out of the 87 tab then relay is bad. 87a shouldn't be hooked up unless you want something to be powered up before you pull the headlight switch (and then power goes away). Also 85 and 86 are for the coil, it doesn't matter which one is ground as long as 1 is ground and 1 is power.

Check the relay power/ground with the connectors on the relay tabs, just slightly move the connectors down and make sure you don't touch anything else with the test light while testing.

Lastly and I can't stress this enough, buy good quality relays.

 

I'm betting 86 has no power to it.
Are you pulling the power for 86 from the headlight switch, or from the dimmer switch?

If you are pulling the power from the dimmer switch, you need to be sure the dimmer switch is good, and you are getting your power from the correct wire.
Power to the dimmer switch comes from the headlight switch. Then that power is switch to either the high beam side or to the low beam side. The high beam side should provide the power for #86 on the high beam relay, and the low beam side should be the power to #86 on the low beam relay.

If the dimmer switch is defective, you may not have power to either #86 terminal on either relay. Gene

 

87a will have power on it, terminal 30 ( battery power ) goes right through the relay and out 87a. Once you switch the relay, 87a shuts off, and 87 turns on. Here is a quick and easy drawing. View attachment 5231355

 

So I just checked and I’m getting 12v at pin 30 but not getting anything at pin 86 when the headlight switch is on. So I screwed something up, because the headlights worked fine before I wired in the relays yesterday. The entire electrical system is brand new, I completely rewired everything about a year ago, all grounds are good, new stock headlight switch and new dimmer switch.

I tapped the relays into the low and high beam headlight wires under the hood near the core support just before they split left and right. Any ideas where to begin troubleshooting?

 

Figured it out. Junk dimmer switch. Go figure.

thanks guys!

 

Glad you got it sorted!

 

Happy you got it figured out.
Thank You for letting us know. what you found. Gene

 

I'm going to throw a curve ball here, from experience in using relays. It's an echo of what's said above- good quality relays are essential. A lot of the plastic ones aren't rated for continuous maximum, check the data sheet. I've had "30A" relays go bad and the thermoplastic they're made from loses integrity when they get hot.
If you drive a lot, fork out the extra for a decent screw-terminal relay with a continuous contact rating for the low beam position. One of the metal can and impregnated pressboard types.

The second thing to watch out for is moisture ingress. There's a good chance the relay will be connected to the battery positive terminal permanently. The metal parts inside are usually steel with a cadmium coating which is great until it has an ionic charge on and there's moisture in the air, because it turns into powdery oxides which can cause the contacts to gain resistance and get hot or fail.

So, life with relays can be bright and wonderful (one for low, one for high) but choosing them is important, positioning then is equally important and disconnect both terminals of the battery if you're going to park the car up for a while.

Phil

 

Excellent schematic.

 

On a standard ISO (international standards organization) Bosch style relay the center terminal labeled 87A is hot (connected to pin 30) with the relay de-energized or not powered. When powered (energized) terminal 87 is hot (connected to pin 30). Pin 30 is normally connected to constant battery voltage with a fuse. There seems to be some confusion about two (2) 87 numbered terminals, I have seen relays that have terminal 87A deleted during manufacturing so no confusion could exist. Hot Rod magazine did an article a couple years ago and got it wrong stating you could connect a second horn to terminal 87A, you could but it would be on constantly Until you hit the horn switch, not exactly how I would want my horn to work.

 

I'm so glad you replied. This is why people have left.

 

This is how I did mine

 

one night i was out joyriding in my father inlaws p/u . long before he was my father inlaw . or i had a lic. for that matter . anyway ,dark , twisty , country . hit the dimmer and no lights . im not sure if there was a relay or not . but this thread brought that evening to mind !! i think with good wire/switch .relays are not required/mandatory ? it seems things like quality dimmers are getting rare !!

 

FYI, the OEMs have used the generic 'bosch type' relay for years in various applications. My old f150 must have a dozen of them. Must be good quality since it is a 97 and none have failed. Bet you could pull a bunch of them at your local you pull-it for almost nothing. My local will sell a wire harness for two bucks a foo and fuse box w/plugins for 8 bucks. Great source for high quality electrical stuff. Lots better than the stuff sold at the local parts store or eBay.

 

There is more than one way to wire the headlights. My old Toyota pickup had 4 fuses to the 4 headlights. If there was a problem with one of the lights, you still had the other ones to see at night.

 

Loads of ways, absolutely.
If I remember it right i think a number of japanese manufacturers switch the negative side of the circuit instead of the positive, i.e. the lamp gets +12V constantly, and the other pole of it is grounded when it's turned on.
As long as the lamps are separate (i.e. not combined high/low bean in one bulb) that would allow one fuse per lamp, despite having just one relay for low bean and one for high beam.