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1993 Lift Pump Relay Upgrade, '95 Confusion

D

DieselAmateur

She ain't revved 'til the rods are thrown...
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I know this subject has been covered before, but wanted to share my own adventure if for anything else to have a reference online for when I lose my notes

So on the 1993 dump truck that is nearing completion, I wanted to do the lift pump relay for obvious reasons. The previous owner had also cut into the factory wiring and spliced in a switch that was in the cab for turning on the lift pump, which bypassed the oil pressure switch which is good for the life of the OPS but a safety issue as fuel will keep flowing so long as the switch is engaged with the key on.

The 1993 lift pump system is different from 95+, where to the best of my understanding the factory lift pump relay on the passenger side firewall is energized and sends power to the lift pump only when cranking, whereas once the engine fires up and the key is returned to the run position that relay switches off and power is then sent to the lift pump via the grey wire on the oil pressure switch.

Wiring the relay is straightforward and easy, standard 5 pin relay goes:

85- ground, ring terminal grounded to firewall
30- 12v source for the relay, ring terminal gets power from stud on passenger side firewall
86- trigger wire, here the OPS grey wire, cut a few inches from the OPS connector and spliced to 86 on the relay
87- switched power to lift pump, I connected this to the other end of the gray wire cut at the OPS

With all that done, I recognized that I still didn't have a wait to start feature, which I'd like to have, so I wandered over to my parallel parked '95 to investigate. This truck has the upgraded relay purchased from a vendor, and since I'm sharing details I don't want to name the source and take away business, but its wiring is the opposite of how a relay is normally wired and threw me for a loop. It functions as it should on the truck so it clearly works, and my ultimate goal here is to make sure I did everything right on the '93 as it currently doesn't match what is on the '95

So on the '95 with wait to start, this is how the relay is wired:

85- Two wires connected to terminal 85, one from the glow plug side of the glow plug relay, and one that gets power from the OPS, essentially the same thing as the grey wire on the '93
30- One wire connected to the + terminal at the lift pump, so sending power to the lift pump
86- Ground
87- 12v all the time power with an inline fuse, connected to one of the studs at the fuse center block on the driver side

So as you can see, the '95 relay is wired totally a$$ backwards from what most instructions call for. Trigger and ground wires are switched, 87 and 30 are switched.

I've read that 85 and 86 can be interchanged as just one or the other energizes the relay, and that in some cases where there is a diode in the relay you are actually supposed to use 86 as a ground and 85 as the trigger, but I see no diode symbol on the cap which has the relay diagram

What really confused me was that the switched/ energized terminal (normally 87) here seemingly has power all the time, and that the terminal for power source is the load function sending power to whatever is turned on when the relay is energized.

As stated the '95 relay functions normally with this seemingly reverse configuration. So my question(s) are:

If/ when wiring a relay where 85 and 86 are reversed (85 for trigger, 86 for ground) is it required to also swap the functions of terminals 30 and 87 too? Or can one or the other be left alone (85 for trigger, 86 for ground, 30 as 12v power source for relay, 87 for power load/ output to whatever is activated by said relay)

The wait to start feature is achieved by using the glow plug side of the glow plug relay as the trigger wire. So as my '93 is currently wired, will I achieve the WTS by connecting the glow plug side of the relay to terminal 86? Or do I have to re- configure everything to match the '95.

I don't have batteries or the fuel system hooked up in the '93 yet, so I am unable to test and would rather be certain my wiring is correct before accidentally frying something.
 
I wouldn't try matching the 1995.

I'd just wire the 93 by the numbers.

Can you repair the hacked wiring and make it plug and play like Leroy's?

I also install a toggle switch to run the lift pump in demand while changing the fuel filter or doing diagnostics.

I avoid cutting and splicing as much as possible anymore
 
MrMarty51 said:
Hook the trigger signal wire to an ignition switched power source.
That way the fuel pump is energized for as long as the ignition switch is in the run position.
Click to expand...
He's trying to maintain the safety factor of the oil pressure switch/OPS.

IF IN AN ACCIDENT, wired hot, the pump will keep running until power is killed or the battery dies.

If there's a leak it'll empty the tank.

I triggered from.the glow plugs, the toggle switch and the ops.
 
@jrsavoie the '95 is Leroy's. That's what has me somewhat confused, it's not wired "normally" but functions as intended.

Sounds like I can trigger from the glow plugs too to get pre start prime if you did the same and keep my wiring standard. Still don't understand how Leroy's works with the other pins all mixed up.
 
DieselAmateur said:
@jrsavoie the '95 is Leroy's. That's what has me somewhat confused, it's not wired "normally" but functions as intended.

Sounds like I can trigger from the glow plugs too to get pre start prime if you did the same and keep my wiring standard. Still don't understand how Leroy's works with the other pins all mixed up.
Click to expand...
That's kind of different.
Maybe it has to do with backfeed from using one relay for both the prime feature/ glow plugs & the OPS.

I used a separate relay for each. And just tied the outgoing power wires together. I don't know how to go about tying the diode in.
 
iirc both the 95 and 93 have the ops wired the same to turn on the lift pump. but both are different on the glow plug controller circuit. I ended up ditching the glow plug relay on my 93 and wiring in one from a 95 along with using a time delay relay to control how long the WTS was on.

for the 95 there is a yellow wire that comes from the PCM which when 12v + is applied to this yellow wire, the GP relay engages. I wired in my own relay for the lift pump using the OPS as the trigger for the relay, but also on the 5 pin relay, I used the center 5th pin to run off the glow plug relay so when the GP's were on, the LP ran for that short time.

I can put together a diagram if you want. the only difference between my 95 and 93 trucks are the 95 still has the PCM controlling the GP's and the 93 uses a time delay relay on the GP controller. every time you cycle the key, the GP's run for 8 seconds.
 
Thanks for the input gents. @dbrannon79 Thanks for the tip on the yellow wire coming from the PCM, not an option for the '93 though. I was wondering if the '95 relay was wired differently because it was also tied to the glow plugs. I think I could achieve the wait to start feature on the '93 by connecting 87a to the glow plug side of the relay as you did. However I would have to have pin 30 be keyed on power, not 12v all the time from the fuse block as it currently is since 87a and 30 are normally closed together so wiring them together would send power to the lift pump with the truck off.
 
the issue with the 93 GP system is there is no way to energize the GP controller manually as it has iirc a built in trigger that senses the load from the GP's. idk how it all works but I know others like @Will L. can explain how the older GP controller works. on the 95+ controllers it's basically like a starter solenoid

to keep the 93's GP system in tact, you can run a wire from the side of the controller that sends power to the GP's with a diode preventing feedback to the 85/86 terminal that uses 12v+ to trigger the LP relay. this way when you turn on the key the GP controller will send power to trigger the LP relay till the GP's turn off. once started and running the diode will stop power from feeding from the LP relay and ops into that side of the GP controller which would send power to the GP's. without the diode it would burn out the ops and possibly melt wiring along the path.
 
it works the same on overriding the GP controllers with an push button in the dash. on the older (93) GP controllers, there is no way to override it to force the GP's to stay on longer other than using another relay like a ford starter solenoid to short across the two large terminals of the GP controller. for the newer (95) GP controllers, it's simply wire that push button to apply power to the yellow wire on the GP controller which forces it to act like a big relay it's self. if that make better sense!

earlier GP controllers sensed resistive load from the GP's. there was a part inside that once it got hot the controller shut off and it was done till it cooled. the colder the outdoor temp was, the longer it would stay on warming the GP's. on the newer ones it was all controlled by the PCM reading the ECT and IAT sensors to time the GP's the newer GP controllers are nothing more than an overgrown fender mounted starter solenoid!
 
dbrannon79 said:
the issue with the 93 GP system is there is no way to energize the GP controller manually as it has iirc a built in trigger that senses the load from the GP's. idk how it all works but I know others like @Will L. can explain how the older GP controller works. on the 95+ controllers it's basically like a starter solenoid

to keep the 93's GP system in tact, you can run a wire from the side of the controller that sends power to the GP's with a diode preventing feedback to the 85/86 terminal that uses 12v+ to trigger the LP relay. this way when you turn on the key the GP controller will send power to trigger the LP relay till the GP's turn off. once started and running the diode will stop power from feeding from the LP relay and ops into that side of the GP controller which would send power to the GP's. without the diode it would burn out the ops and possibly melt wiring along the path.
Click to expand...

I think we're saying the same thing, tying into the glow plug side of the relay (side closer to the passenger side, when looking at the engine from the front it's the terminal to the left) would energize the relay with the glow plugs on. Good point on the diode to stop backfeeding to the relay. I'll have to try to upload a picture but I think that's what the 95 relay has on both the trigger wires. The two wires broke away from the relay socket when I was struggling to unplug it and in the socket are just two thin solid pieces of wire. I was confused but now I think I'm seeing two broken off diodes.

So I'm still confused by the '95 having stuff a$$ backwards, but now I feel confident that I can safely wire the '93 with wait to start and not fry anything. Thanks so much for the help, not having a running/ electrified truck really limits what I can troubleshoot.
 
DieselAmateur said:
. The two wires broke away from the relay socket when I was struggling to unplug it and in the socket are just two thin solid pieces of wire. I was confused but now I think I'm seeing two broken off diodes.
Click to expand...
on your 95, the wires that broke away, your talking about the long connector (small wires) on the GP controller? should have just three wires in a connector, don't think they used diodes but there should be a pinout for it if you need. I can find one so you can put that one back together if needed.
 
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