Anyone Know How a Relay Works? (1 Viewer)

[1979 FJ40ish]

Last fall I installed a Fastronix 900-005 relay kit, in my 79 FJ40, that I use occasionally to operate an electric fuel pump to prime the engine. I doubt that it’s been used more than 30 times since it was installed. When I tried to use it the other day the pump would not run.

I verified that I have 12-volt input to the relay and a good ground. I hear the relay click when I push the switch to activate it, but the 12-volt pump it’s connected to does not run. When I put 12-volts directly to the pump it runs. When I measure the relay voltage output (terminal 87) I was only getting about 8.5 volts.

I assumed the relay failed so I purchased and installed a new 900-005 kit yesterday. Fresh out of the bag I’m having the same problem with the new relay that I had with the first one except now I’m getting something less than 8 volts on output terminal 87.

The most recent changes to the FJ40's wiring were made long before the 1st relay stopped working. Do you have any thoughts on what would cause the relay’s voltage output to drop? Is there a way to test the relay itself? Could something else other than the relay cause the voltage to drop?

 

[RockDoc]

Is full voltage being fed to the #30 terminal?

 

[3_puppies]

the relay ground has no effect on the thru voltage, 85,
the control voltage has no effect on the thru voltage, 86,

I go with @RockDoc on the thru voltage, 30,

 

[rghouse]

My experience with relays is if they click, they’re working, and since you even tried replacing then I think you’ve eliminated that. Some thoughts:
-What else is on the circuit, could something else be drawing power during priming attempts?
- what is the voltage at the pump? (Resistance from relay)
-what is the amperage/wattage at source (30) red input? Volts don’t tell the whole story...
- is battery in good shape?
- what are the amps/watts requirements of pump?
-are there any aftermarket or cheap Chinese parts on the power side? I’ve had random voltage drops from a timer I setup on a generator auto-start. I had to use a higher rated timer (16 volts).

I used to hold down the gas pedal for about 3-5 seconds then pump it a bunch while cranking it over. Pull the choke out all the way, if it didn’t fire, push the choke in some. Then adjust choke as necessary during warm up. Did the priming pump help that process along? Assuming this is a 2f...

 

[Steamer]

Voltage will drop with a bad connection. Did you change the socket with the kit as well?
Did you check voltage at 87 with the pump disconnected and switch on?

 

[Living in the Past]

Get a piece of wire and attach it to the positive battery terminal. Then touch the other end to terminal 30/86/87. If the pump does not run when you touch any of these terminal one at a time touch the wire to the pump to the terminal where the wire from post 87 on the relay goes. If the pump does not run for any of these it's neither the pump ground or a bad pump.

Report back what you find. By all these tests should be easy to figure this out.

 

[Solace in Solitude]

Best relay wiring info I’ve found

I’ve used it religiously for everything from electric fuel pumps to DUI ignition.

As stated by others, bad connections and bad grounds can cause voltage drops.

I’d do the tests above... and

Make sure battery is charged

Check the fuel pump Connections

Check the relay connections

Make sure fuel pump has a good ground.

Make sure relay-30 is fed from battery+

Make sure relay-85 has a good ground.

 

[1979 FJ40ish]

Thanks for all the feedback. I’ll try to address some of the questions/comments.

First, let me restate that the relay/pump worked since they were installed 9 months ago and only stopped working about 2 weeks ago. There were no changes made to the electrical system since they were installed.

The power source for the relay (terminal 30) is an auxiliary fuse block installed on the firewall. The fuse block is fed directly from the positive battery terminal. There is nothing else on the circuit. The voltage output on the fuse block terminal that powers the relay (terminal 30) is 12-volts.

Per the pump’s installation instructions, I installed a 3 amp inline fuse on the terminal 87 output lead between the relay and the pump.

The next 2 steps were performed with the inline fuse removed from the fuse holder.

When I said I was only measuring around 8 volts on the relay output I was measuring it at the relay side of the inline fuse holder (input to the fuse).

When I said the pump runs when connected directly to a 12-volt power supply I attached a lead to the output side of the inline fuse holder (pump side) and then directly to the positive terminal on the battery.

I checked the ground by connecting the terminal 85 lead directly to the negative terminal on the battery.

I did NOT replace the relay socket when I replaced the relay.

When I installed the relay and pump, I soldered all the connections and then protected them with heat shrink. Which is why I was reluctant to replace the socket. These connections all seem sound and wiggling the wires has no effect.

The FJ40’s battery is in excellent condition.

As for measuring amps, wattage or resistance I’m pretty much clueless. I have the meter but don’t know how to take these readings.

I think I’ve covered most of the comments and questions you raised.

Again, thanks for your comments.

 

[Steamer]

Since your socket is all soldered neatly in place, I would remove the relay and jump from battery positive to 87. This will narrow it down. If pump runs, all is good between relay & pump.

I like this diagram.

 

[Steamer]

And if the pump runs, next would be to jump 30 to 87 on the socket with relay removed. This would just simulate what the relay does when energized.

 

[3_puppies]

after reading this again, I question what you're doing with the pump.
priming the system? there should be no need for that. might be simpler to fix the actual issue versus a masking it with a band aid.

 

[1979 FJ40ish]

I had some time today to get back to this.

When I jumped between the + side of the battery and socket terminal 87 the pump worked.

The voltage at socket terminal 30 was 12.3 volts

When I jumped between socket terminals 30 & 87 - the pump did NOT work

When I bench tested a new relay socket by jumping between terminals 30 & 87 I had continuity

I replaced the relay socket and now the pump is working again.

Thanks to all for helping me diagnose this issue.

 

[Solace in Solitude]

Glad you resolved it!!

I'm curious, NO insult intended... but, is it possible that you inadvertently hooked your 87 wire to 87A?

For those who aren't familiar with relays... or 5-contact relays... 87A is the opposite of 87. e.g.:

relay-87 sends relay-30 voltage when relay-86 (trigger) receives voltage

relay-87A sends relay-30-voltage when relay-86 (trigger) does NOT receive voltage

 

[1979 FJ40ish]

Solace

We've never met but it seems like you know me. Mixing up the wires is certainly something I'm capable of doing but in this case, that wasn't the problem.

It seems strange the socket would go bad. I have it mounted on the passenger side of the cowl inside the engine compartment. I wonder if it got too hot. If I have the same problem again I'll relocate the relay.

 

[Solace in Solitude]

I have a couple under the hood, PS side... no prob. Also 3-4 under the dash. One of those failed.

Prob just poor quality control.

 

[Steamer]

OP stated it ran close to 30 times before it failed so it seems it was wired correctly. So it's looking like a socket failure or bad connection. If you still have the old socket, you could check it for continuity from terminals to wire ends and help solve the mystery. And if it checks out good then ya just gotta put the old relay into the old socket and check it out.
That's if ya really wanna know. Bottom line, it's working now.