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I finally got around to doing my OPS relay today. I found in the search that there weren’t any pics of this so took my camera along and snapped some. The first pic is of the OPS location. The second pic is of the OPS plug and the wire colors. The third pic is of the items I used to do the project. The fourth pic is of the wires cut and crimped.

The length of the extension wires were 24“, I removed the convoluted tubing from the OPS wires before I started cutting. my wire colors for the relay extension were :

Orange for the hot: I cut the orange wire from the OPS plug about 3” from the plug and tied in the orange extension wire. Crimped and shrink wrapped it.

Gray for the OPS plug: approximately 2.5” from the plug I cut the gray wire. The wire from the OPS plug I connected the gray extension wire. Crimped and shrink wrapped.

Light purple for the LP: on the cut wire going to the LP I connected the Purple wire. Crimped and shrink wrapped.

Brown for the ground: The brown ground wire is much shorter because it is just ran to the relay’s mounting screw.

My pics don’t show the shrink wrap installed on the wires (I thought I had took one but this was the time the grandson decided to interrupt me). The fifth pic is of the wires from the OPS re-loomed and the relay wires Loomed. I decided to mount the relay under the electric shroud pic # 6 on the passenger’s firewall pic # 7 . It seemed to be the most likely place to put it. Being that the factory saw fit to have already put holes there and the other relays were there as well. I mounted the ground with the same screw I mounted the relay with. Then replaced the shroud.

The relay is numbered and the extension wires hook to the relay in this order. #30 is the orange power wire (by the way this wire is hot with key off don’t let it ground out. Please don‘t ask how I know). #85 is the brown ground wire, #86 is the gray wire from the OPS and #87 is the purple wire to the LP.

Staff Edit:

Oil Pressure Switch: Replace OPS with AC Delco D1808A

Relay Parts Options:
Relay: NAPA - AR143
Relay Connector: NAPA - ECH EC23 or Relay Connector (with mounting bracket): NAPA - ECH EC38
"Marine" weather proof crimp connectors with heat shrink "built in". Available at O'reillys and other parts stores. Use heat gun. Sample: Click Here. These connectors are available in smaller quantities.

1992-1994 Trucks: Instead of tapping the Orange wire, get 12v for the relay from the Power Block located on the passenger side of the firewall.



Remaining pics in post 2
 

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Discussion Starter #2
Remaining Pics

had to do 2 posts of pics
 

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Ok I might have misseed this in previous discusions,, buy WHY is this needed or wanted? What does the relay help do? Not being a dink here,, just wondering,, and figured it would add to the helpfullness, of this thread! Great pics by the way, and way to be a team player!!
 
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Nice job with the Pics, Schwind! (heading over to FAQ...)

The OPS is a safety device in the Fuel system of the 6.5. It controls current running to the Lift Pump, by sensing Engine oil pressure. When there is Oil pressure, indicating a running engine, the OPS sends 12v curent to the LP, which runs and lifts fuel up to the IP.

When the engine oil pressure drops off, as in a crash or rollover and the engine stops, the OPS cuts the current to the LP, stopping fuel from being pumped out on the fire, if ya know what I mean.

When starting a 6.5, expecially the OBD-I models, the ECM sends 12 v to the LP while the truck is cranking, to start the truck. Once the thing starts and the Oil Pressure comes up, the OPS handles that duty.

A truck will run without a functioning OPS, but not well... it's hard on the IP to suck fuel up from the tank, and starvation is a common result when stepping on it.

Again, nice job, Schwind!
 

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What did you crimp the wires together with?

Going to put a bypass switch on it also, to fill the filter when changing it out?

Nice work!

Now you need to do the headlights.
 

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Putting a relay is to unload the power supply circuit to the lift pump passing through the OPS.

There are 2 circuits in the OPS : 1 for the gauge, 1 for powering the lift pump.

The orange wire is the common main 12v (hot at any time IIRC), the white is to the oil pressure gauge in the cluster, and the grey is the 12v supply to the lift pump.

Inside the OPS, the lift pump power supply circuit is "poorely" designed, let's say not strong enough, and that's the key of the common failure on OPS.

That' why putting a relay will unload the OPS : the grey wire is used only to trigger the relay, the relay then supply power to the LP---
 

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Nice job, Ive been planning to do the same thing as soon as I buy a new OPS.
 

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Discussion Starter #8 (Edited)
What did you crimp the wires together with?

Going to put a bypass switch on it also, to fill the filter when changing it out?

Nice work!

Now you need to do the headlights.
I used uninsulated butt connectors and crimp them with my bluepoint forged crimpers. With the intentions of using heat shrink for insulation.

As far as filling the FM after a filter change I have found that putting the gear shifter in drive and then turning the key to the start position works pretty good. It runs the fuel out of the bleeder valve pretty quick.

I was thinking that I may just buy the headlight harness from LMC being that they have already perfected it. I don't know that much about the circuit the headlights run off of. That will come when more money is rolling in. :rolleyes:
__________________

Seems like others have chimed in on the reason why with all the right answers. I think that the lift pump is working/running better this way too. I seem to be getting more black smoke at WOT than before. I think that the OPS circuit is restrictive on the voltage or should I say the amperage going to the LP.
One thing left to add to the question of why is that it will help extend the life of the OPS being that it is not running as much voltage through the circuit.
 

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Where might one purchase such a relay?
 

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Probaly at the Zone!

Ok I see now, I to had to replace my OPS a month or so ago, It seems that one of the 2 Internation Diesel remans being installed last summer, had the engine swingin on the cherry picker and I think the Mech "bumped" the OPS against the firewall, it still worked, but when I put a new Glow relay in, I seen that it was loose. As I was inspecting just How loose it was, it fell apart in my hand. So off to Autozone to by the OPS. I guess this will get added to the list of stuff to do to the truck the next time I get a few hours to spare, without the wife/kids pulling at me wanting me to do things with/for them!
<yeah yeah, I know good luck with that!!> :whip:
 

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There are a bunch of posts concerning AZ OPS failures. Get a Delco!
 
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Discussion Starter #12
Where might one purchase such a relay?
I used a bosch (brand name) relay it was about $8.00 at the auto parts store local company. Had to ask for it by name. All the big branch stores had unknow brands.
 

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ops bypass switch

i have 98 gmc 6.5
has factory auxillary buss with fuses at battery under hood
i just ran neg to pump and pos from spare fuse to sw on dash and down to lift pump
15 minute job
works great!!!!!
kevin
 

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i have 98 gmc 6.5
has factory auxillary buss with fuses at battery under hood
i just ran neg to pump and pos from spare fuse to sw on dash and down to lift pump
15 minute job
works great!!!!!
kevin
Sorry to rain on your parade, Kevin... I have no doubt it works great, but you just bypassed a fairly important safety feature...

The OPS shuts off the Lift Pump in the event of a crash that stops the engine, or when you shut off the key. Without it, the LP keeps running. Let's say you hit a pole... the impact seals the doors, a small fire starts... and the LP keeps on pumping fuel. If you can reach the switch (or remember to do so), you can shut off the inferno... if not...

I hate to do the doom and gloom thing, and I have bypassed safety stuff before, too... but this circuit is easy and cheap to bolster with a relay, taking the load off the OPS and still keeping the safety feature active.

I'd change it back, if I were you.

Just my $.02...
 

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Great writeup!!!

My suggestion is to put it in the FAQ as part of LP/OPS link?
 

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Discussion Starter #17
Here is a pic of how the relay works. it is not with the OPS wiring.
 

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Discussion Starter #18
This pic is how I wired the relay.
 

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Hey schwind,

not to hijack your thread.
Just to tell I just finish my relay mount.
I wired it exactely as you show.

What's funny now, it's that when I shut off the engine, the lift pump still goes on and shuts after a while (10 seconds when cold), I believe untill oil pressure has gone down and release the switch inside OPS wich opens off the relay.
 

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Discussion Starter #20
Hey schwind,

not to hijack your thread.
Just to tell I just finish my relay mount.
I wired it exactely as you show.

What's funny now, it's that when I shut off the engine, the lift pump still goes on and shuts after a while (10 seconds when cold), I believe untill oil pressure has gone down and release the switch inside OPS wich opens off the relay.
Mine has a delayed shut down as well but its just a few seconds. I believe it is like you said, the OPS registering oil pressure for a short time after shut down.
 
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