Had a weird one today. Finishing up the wire tidying under the hood. Put my relays back in the headlights. (I am running a pair for the hi/lo beam relays like the FTE tech article). Anyway, I put the relays in today and the headlights are on all the time. Pulled a couple more from the drawer and all were doing the same trick. So I got sidetracked instead of proper diagnosis and start pulling down my headlight switch, dimmer switch and unwrapping the harness. Everything tested fine so I check the relays like I should have in the first place. All three had continuity from terminal 30 to 87A when removed from the harness. Shouldn't it stick and send juice out both 87 terminals? Not just one side.

All three relays only have a few hours use but have been idle all winter in a drawer. All three are also cheapo Auto Zone relays too. I found one brand new relay and problem fixed. Only things I can think of is they were definitely run a considerable time with the headlight grounds very loose as I jumped around the truck over the months I was wiring from time to time. I have also jump started the truck a bazillion times from running it dead while messing with electrical.

I am nearly certain I am wired correctly as the lights worked fine before and now. I can always jumper them if they failed me on the road again, just curious what kills relays. Bad ground? Power surge? I have changed Bosch relays countless times, but never gave the reason for failure a second thought.

 

Dwayne,

Typical Bosch relay is a 4 pin normally open, right. With no juice applied to 85 and 86, 30 and 87 should be open circuit. If there is continuity with nothing across 85 and 86, the only thing I can think of is that the contacts are welded shut. it may be interesting to rip one of those failed relays apart and see if indeed the contacts are closed or open.

 

"it may be interesting to rip one of those failed relays apart and see if indeed the contacts are closed or open."

I did and they are not welded. Most automotive Bosch relays are 5 pins with 87 split into two. But 87 and 87A are always supposed to have continuity, or so I thought. But I am only seeing juice out one leg of the 87 on the "bad" relays. It makes no sense, I'm confused. Whenever electricity makes no sense, it's usually a bad ground causing a backfeed, or low voltage. All our Army trucks have dozens of Bosch relays. I'll study a good one tomorrow.

 

On a Bosch type relay-5 pin style:

30 = power in
85 = ground or power to trigger
86 = power or ground to trigger...if ground is used on 85 use power to trigger on 86

87A = normally closed-if no power to 85 and 86 then 30 is connected to 87A

87 = gets power when power is applied to 85 and 86

here is a few links to look at:

http://www.classictruckshop.com/club...osch/relay.htm

http://www.underthedash.com/relayindex.html

Hope this helps

I used to do automotive audio and security now doing the Home automation thing

Glack

 

Sorry, didnt read all of the post....usuall cause for relay failure is running them at he max for extended periods of time..and the use of inexpensive relays. try to use bosch and potter brumfield relays, check the temp of the relay after a few minutes of use to see if it is getting warm. if it gets warm/hot the item being driven from the relay is drawing max current and will burn out the relay for sure, the potter brumfield is rated at 40 amps(the ones I used) and never saw one come back failed. the bosch are pretty good, ran a few at max and had them come back with blown fuses on the power lines and a couple with meltd cases

Glack

 

Thanks Glack, despite what I said a few posts ago, I have them wired correctly. I'll pick up some good relays today. I bought the last ones at the first place that had them handy. Autozone I believe. Most of the little guys are gone and now I have to go to special trouble to get a good electical part. But it's usually worth it in the end.

 

fenders, I too recently followed the instructions from the website article for headlight relays and mine are working great. I too used (2) of the $4 models from Autozone. I know that you are 100% sure that they are wired correctly, but it makes me wonder. Because, when I put in my horn relay 4-5 months ago, there was an odd fact about it. When the power wire is connected, the ground wire has power on it also. Then when you ground the ground wire by puching the horn button, power is passed to the horn wire. So, if I would have accidentally hooked up the horn to the ground terminal, then the horn would have sounded as soon as I hooked up the power wire. Hmm, just makes me wonder. Please take no offense if I'm way off base here. But it is a long shot that multiple relays could all go bad at once. Just my humble opinion of course. Good luck, John

 

OK

Mystery solved. Everybody is right to some degree. My truck is wired correctly. The relays did not fail. I knew it wired OK because they worked for months. Here's the deal and I am ashamed to admit I did not know this until today.

All Bosch style relays are NOT the same. I wired for relays that have two # 87 terminals. Like the FTE tech article outlines. Both terminals have continuity with each other so it's all or nothing. The other style relay has an 87 and an 87a terminal like Glack describes. One is hot without power on the trigger wire (85). And it flips to the other when you apply power to it. You never get power from both 87 and 87 at once. So as luck would have it I had power to my left lo beam and right hi beam. Which made it a bit more confusing to diagnose.

I could just piggyback wires on one terminal and it would work with these 87/87A relays, but I am not going to trust my headlights to cheapo relays. I've had way too many of them fail and don't want to deal with it.

 

I'm starting to see a pattern here. I remember it wasn't too long ago when it came out that fenders hated those"cheap Grant steering wheels." Now it's "cheapo relays." Just kidding, I'm glad it was an easy fix. John

 

You got the wrong man John. You're looking for 4speed. Grant wheels rule! Accept no cheezy imitations.

 

Well I appreciate the education as I learned something new as well. a 5 pin bosch relay is a SPDP switch. i have never had a need for a relay with one output hot when deenergized and the other hot when energized. Neat.

 

"You never get power from both 87 and 87 at once."

Change that to "you never get power to 87 and 87A at the same time. That should make the explanation above make more sense. Any relay with two 87 terminals will power up both spades at once. At least I would sure like to think that's the case.

 

the dual outputs on 87 and 87 I believe were called ti green stripe relays, they were in a metal housing and actually had a green stripe on the case..maybe Im wrong but thats what memory says...has been a few years too

You would use a DPST type relay-double pole single throw relay

Sounds like you figured it out


Glack

 

Sorry fenders, I thought you were the anti-Grant. I stand corrected, John