Had a relay go bad in the dunes, put a spare in and still wouldn’t start. Had to wire the fuel pump off the whip light. Ran it for two trips like this. Checked it again and now there’s power to the pump from the computer. My question is, do relays reset themselves?

What type of relay is it?

Name Brand.....4-5-6 wiire relay?

Bosch. Not sure how many wires. There are multiple relays wired together.

a relay is basicly a electrical switch. Nothing to really reset like in a circuit breaker. On a normal say Bosch relay you have the two side pins 86 and 85 and you have the three center pins 87a 87 30. When 85 and 86 get power and ground what ever you have attached to 87 will connect to 30 when it is not powered 87a is connected to 30. How did you know the relay was bad? Sounds to me if it still did not work that the relay was fine and you may have a power issue before the relay. If it is loose somewhere it may have shaken back to a place that it is getting power again. Also it is pretty rare for a relay to fail. I would trace the power from the relay back and see if you find the problem.

Now that I have power back to the pump with the back up relay I re-tried the old one and no power. Do you think one of the other relays have something loose inside causing failure at times?

Here's a diagram of a Bosch relay. They come in many types, and are used in quite a few different vehicles. Ford's version is a gray relay with no mounting ear, and is used in the new underhood wiring modules. GMC and Chevy uses them too, but are usually black. There are look-alikes too, but the numbers on the terminals give them away. Most after market relays will have a mounting tab for mounting it with a screw. Always mount them with the terminals facing down, or they will get water inside and fail.

The innards of the relay. When power is applied across the 85 and 86 terminals, current flows through a coil of small wire. This wire is about 100' long, and is usually 28 gauge wire. This builds up a magnetic field in the bar it's wrapped around, and the steel plate snaps to it. When the power is off, the spring pulls the plate back away from the magnet bar. The "click" is the plate slamming into the magnet as it turns on. It doesn't "click" when turned off, because the plate swings away from the magnet without hitting anything.
Note: When the power is applied, the coil sets up a magnetic field in it's windings. When the power is removed, the field collapses, and a reverse current of high voltage will "kick back" This is called counter EMF, and is how your ignition coil works. If your fingers are across the coil terminals when the power is removed, you will get shocked!!

Below is a couple of circuits to help understand how the relay works in real life. Relays are used to transfer high current. A Lot of vehicles make use of the ground-to-turn-on circuit. If one if the relay coil terminals have battery power all the time, the ground-on circuit is how it's wired. Most horn relays are wired in the ground-on method. The steering wheel contact touches ground and turns on the horn. The horn relay is used because the 15-20 amps from the horn would arc and quickly destroy the contacts in the steering wheel

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If you have the backup relay in now and it is working and you switch it out with the original and it doesn't work sounds like you do infact have a bad relay. Now you need to figure out why it didn't work when you first put in the second relay. I'm guessing that you still have a loose connection that can cause arc inside the relay which can be hard on them which could have caused failure #1. It just doesn't make sense that relay two didn't work at first and then started working.

If you have a factory GM pcm then the fuel pump driver in the computer is controlled by a "quad driver module" which monitors the line voltage at all times so as to know if the wire shorts, develops an open or actually operated something. This is always a ground supplied by the pcm and if a low voltage occurs like say a shorted relay then the driver would set a code and not supply the ground to that circuit. It will reset as opposed to older ecms from gm that would ruin it and require replacement. Aftermarket computers may or may not be this way

You lookin for a Job? We could always use another smart Tech here @ my shop..

It’s a factory Toyota computer with a piggyback computer to control timing and air/fuel ratio. So what your saying, is the computer trips like a circuit beaker then resets itself? Will there be a stored code?

Can I ask, when should you use a relay? If you have a fuse, are they still needed? If so, why? I know somewhat why they are used, but dont know when and if theyre needed. Sorry for my ignorance...

relays are used in a few different ways:

1.
to control a circuit or circuits of different or higher voltages IE. you can use a 12v relay to control a 110v circuit or vice versa.

2.
to control multiple circuits at the same time. IE. fans and fuel pump off of different contacts on the same relay .

just remember a relay is not a fuse. it is a set of contacts just like a switch, although the contact will have an amp rating it is still wise to fuse every circuit you have. a fuse is designed to open up the circuit when an over current condition is present therefore preventing damage to wires or components, a set of contacts will burn up when subjected to an over current condition thus destoying the contacts . A fuse is much cheaper and easier to replace than a relay.

Coming from an automotive stereo and security background, I have seen relays used in many different ways. You are probably using the negative trigger fuel pump output from the ECU to trigger the relay, in turn feeding 12v to your fuel pump. The power feeds to your fuel pump through a small contact inside the relay. If that contact gets one grain of sand on it, the relay can fail. if that grain of sand fell back out, the relay can work again.I have found that in a sand car these relays last much longer if you:

1. seal any holes on the bottom where the contacts are
2. mount them vertically with the contacts on the bottom
3. mount them inside a box
4. carry a spare
5. any combination, or all, of the above

and yes, a fuse or manual reset breaker is still needed on all circuits, although there are many sandcars out there that dont use them.

Some good info . Thanks Few more ?'s. Should you replace them after a certain amount of time or trips? Do they wear out? How can you check them?

Can't really check them other than see if they are working. You can't pull them apart to see inside or anything. But if they are sealed they should almost last forever. A couple in the tool box is always a good idea. But it isn't like a oil change or anything. I probably have 50 in my truck I have never had one fail. The sand and water are the two things that could really get them.


Like stated above always still fuse them. They really have hundreds of uses but the main one is say you have a switch on your dash and it can hold say 5amps well the circuit you need to run is say 30amps. The switch uses low to almost no current to turn on the relay which allows the higher current to run to the circuit. The place you see this alot would be like a set of offroad lights.

The Bosch relays have a little breather hole in the bottom and you have to seal it up or it will get sand in it. They seem to work fine sealed up.
Mister outback posted this a long time ago and I checked mine and sure enough there were the holes so I plugged them and they are still working like a champ. I use a lot of relays so I don't have power in my dash, also saves a lot of heavy wires to switches.
THANKS AGAIN OUTBACK
DON~~~

So is it safe to say that a relay is only needed if the amps of the device, be it lights, fans, est., exceeds the amp rating of the switch? Or am I trippen ?

That is one way to look at it. Also you don't have to run the power all the way to the switch, just a light weight switch leg. They just clean up your wiring job also.
DON~~~

Yes and no Basicly that is correct. But say you have one switch in the front and it needs to run more than one thing and maybe one thing needs a positive to turn on and another needs a ground you could use relays for that. They can be used for all kinds of things. Once you have the basics down you can use them for all kinds of things. Like Don said if you want to keep all your high current cables away from the dash. Many security ideas. If you get some diodes and relays you can have all kinds of fun...

This is typical toyota wiring for fuel pump Might check to see if you also have the factory efi relay wired in the same way cause if that relay was inop then you would have no fuel pump relay power.

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Put my mekanik hat away after 20 yrs, having fun now!!

These are great relays sealed and waterproof.




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The main purpose for using a relay in anything is to avoid "bounce" When you run high current through a regular toggle switch the contacts will bounce creating an arc between the contacts. This, over time will create pits. When you power a relay it is slammed on. No bounce or arc. A relay will last alot longer than just running it through a toggle switch. Assuming sand and vibration aren't harming the relay. Relays should be mounted on rubber or some other shock resistance method. A relay is just an electronic switch

What brand name is that? Know where I can pick them up in San Diego?

And one last question...So should I only use relays on my radiator fan and my lights? Are they needed on the guages, and for me those would be oil, temp, and a tach...

Those are Hella brand for lighting but any similar type will work, old gm truck 88-95 fuel pump relays are good also and readily available.

btw: you can tell if a contact is in good condition or not by using an OHM meter.
A good clean set of contacts will have almost zero Ohm's . A pitted or dirty set of contacts will have a high ohm reading therfore potentially causing problems.

correct......but you need to apply power to the coil side or it will show an open (infinite resistance)

Those Hella relays look trick, I hadn't seen those before...... and I just rewired all my relays. I wish I had know about those.

When a relay fails in the middle of the dunes, it's not the end of the weekend. Yes, the controlled device will stop working, such as a radiator fan or fuel pump, but you can quickly fix that, usually. Almost ALL the time a relay fails you can simply take a small wrench and tap the relay a bunch of times while someone flicks the ignition on and off (this is assuming the relays are easily accessible). This will usually always dislodge the grit of sand causing the problem and get you back to camp. I've had relays work for months afterwards, but it's best to replace them when this happens of course.

As for the symtom that started this thread, that's a strange one. It must have been the ECU that did the resetting somehow. Who knows what Toyota does in their computers....

Last month when my fan relays started failing I took the relay apart at home to see what condition the contacts were in with a microscope. Surprisingly they looked very good, they were not badly pitted like I expected. So it was simply a grain of sand that caused my failure, apparently, even though the inside of the relay enclosure was pristine clean.

It's important to seal not only the little hole in most relays, but around the edge of the enclosure too, that's assuming you don't have those trick Hella seal relays, in which case you should need to seal anything. It takes a little patience, but carefully sealing the relay does help keeps things cleaner inside.

I think my next car will have idiot lights for the fans as a backup protection for overheating When I'm having fun playing cat and mouse with others I have a hard time remembering to keep tabs on the temp gauge, and fan failures are common. A red light, one for each fan would help I think.

Here's some pictures. One unsealed, one showing flaws, one sealed.

true unless the set of contacts you are reading are normally closed, then the opposite is true!

Hey Eddy,I have a relay checker.It's a box that you plug a relay into and hit a button.The button makes the relay click open or closed.You can bring some relays by if you want to check them.

I purchased (4) 30 AMP / 12 volt relays off of EBAY so I could finish off my car wiring. Once I received them i was suprised on how many wires were included and why was there a jumper from pins 85 and 86 or is that some type of Diode encased? It also appears to have a smaller jumper from Pins 87 to 30. Can I use these for my car lighting? can I alter these to make them work? Here's a pic of the rear of the relays.

Yes, that is a diode inside the sleeving. It is there to prevent the back emf spike from causing problems in other areas. The diode ( which works like a one way valve) is wired with the cathode connected to the 12 volt side of the relay coil . The anode is hooked up to the other side of the coil that would get a ground from the ecm to energize the relay. When the ground is removed (ie: the ecm decides it's time to turn off the radiator fan) that back emf that tsanchez talked about is dumped back to the 12 volt source instead of getting into places that it should not be. You should cut the jumper between 87 and 30 to use these for your lights. Make VERY sure that the cathode side of the diode and that side of the relay coil gets 12 volts and not ground, or smoke will appear. For your light use, you would just supply switched 12 volts to the side of the coil going to the cathode, connect the other side of the coil (anode of diode) to ground. Then 87 to 12v , 30 to the lights. If you cut back the sleeving, the end of the diode with the line on it is the cathode.

I purchased (4) 30 AMP / 12 volt relays off of EBAY so I could finish off my car wiring. Once I received them i was suprised on how many wires were included and why was there a jumper from pins 85 and 86 or is that some type of Diode encased? It also appears to have a smaller jumper from Pins 87 to 30. Can I use these for my car lighting? can I alter these to make them work? Here's a pic of the rear of the relays.
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Yes, that is a diode inside the sleeving. It is there to prevent the back emf spike from causing problems in other areas. The diode ( which works like a one way valve) is wired with the cathode connected to the 12 volt side of the relay coil . The anode is hooked up to the other side of the coil that would get a ground from the ecm to energize the relay. When the ground is removed (ie: the ecm decides it's time to turn off the radiator fan) that back emf that tsanchez talked about is dumped back to the 12 volt source instead of getting into places that it should not be. You should cut the jumper between 87 and 30 to use these for your lights. Make VERY sure that the cathode side of the diode and that side of the relay coil gets 12 volts and not ground, or smoke will appear. For your light use, you would just supply switched 12 volts to the side of the coil going to the cathode, connect the other side of the coil (anode of diode) to ground. Then 87 to 12v , 30 to the lights. If you cut back the sleeving, the end of the diode with the line on it is the cathode.
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Thanks Subie, excellent info along with the rest of this thread. I've been copying and pasting this forum for reference later. Gary

I have heard that it is good practice to switch the negative side of everything, what are your thoughts on this? Is it safer, more durable, more pratical?

It is a good practice........electricity flows from neg. to pos. (electron flow) Less of a spike when switched on.
That is when you're talking DC

yes theory tells you electrons flow from negative to possitive but standered practice is electricity flows from possitive to negative (a lead from the emf is positive). I think its like that just to confuse apprentices.

oh and by the way kcrtrans where did you get that relay tool?