help with some connector ID

[stackz]

I have my 88 truck harness almost sorted. kinda confused on two connectors over by the fuel pump relay.

I believe the one is the fuel pump test connection?
19791
two prong and has tan/white and a pink/black. both end up at "junctions" in the harness itself. which branch out in various ways.

its weird to me that on one side it would be "fuel pump signal" as per terminal B2 on the ecu connector and then "ign - ecm fuse" as per terminal A6 on the other ecu connector.

what do I even do with this thing? was it ever connected to anything? can I cut it out?

http://www.gearhead-efi.com/gearhead-efi/wiring/747ecm1.jpg
http://www.gearhead-efi.com/gearhead-efi/wiring/747ecm2.jpg

this other one is also a two prong and close by the fuel pump relay. its just as weird as the first one was to me. The orange wire goes to a junction which also goes to that pin on the fuel pump relay in the background. same with the pink/black wire. as above...terminal C16 orange (battery 12v) and terminal A12 (ign-12v fuse). I mean they connected to something at one point I think?
19792
I have pretty much all the other sensors needed hooked up in the harness aside from the o2 which I dont have in my hands yet and I dont have the one side of the coil harness pair going to anything. one side comes from the ignition module. still looking for the rest of the coil harness pic as the one here just sorta cuts off on me right at the 423 WHT line. kinda weird.
http://www.gearhead-efi.com/gearhead-efi/wiring/747ecm6.jpg

also, one last question. how do I depin the ecu connectors? I've been probing one of the pins that I dont need for a bit and cant figure out how it is held in there. been looking with a flashlight and such and cant get it to let go. I'd love to pull a couple wires out....thread them out of the main loom, and then hook them back in so I can separate some of the tangled mess in the middle.

[dave w]

The Fuel Pump Relay and / or Oil Pressure Switch will supply power to the fuel pump. The oil pressure switch is a backup to the fuel pump relay should the fuel pump relay fail. I did an experiment to see what would happen if the fuel pump relay was removed; after an unusually long cranking time (about 12 seconds) the fuel pump came on and the engine started and continued running without the fuel pump relay. I even drove to / from work without the fuel pump relay.

[stackz]

Ok so my thinking was in the right direction but backwards
I thought it was maybe that if it lost oil pressure it would shut off fuel pump to kill engine and save it maybe

[dave w]

I have my 88 truck harness almost sorted. kinda confused on two connectors over by the fuel pump relay.

I believe the one is the fuel pump test connection?
19791
two prong and has tan/white and a pink/black. both end up at "junctions" in the harness itself. which branch out in various ways.

its weird to me that on one side it would be "fuel pump signal" as per terminal B2 on the ecu connector and then "ign - ecm fuse" as per terminal A6 on the other ecu connector.

what do I even do with this thing? was it ever connected to anything? can I cut it out?

http://www.gearhead-efi.com/gearhead-efi/wiring/747ecm1.jpg
http://www.gearhead-efi.com/gearhead-efi/wiring/747ecm2.jpg


The ECM needs to know when the fuel pump is "On" / "Fuel Pump Signal" The wiring for the "Fuel Pump Signal" is spliced into the power wire going to the fuel pump.

[stackz]

ok, but what does it connect to? people on another group think it may be for the alternator but I'm not so sure? I have a 10si alternator on the engine this harness will go on and this plug does look very similar to it though. but I'm not sure?

I'm going to spend some time looking through some diagrams tonight and hopefully figure it out.
19794

[stackz]

ok I think it may have been to some sort of fuel module that I dont need? I cant really tell what else it could have gone to. though I will say there is no black/white on the plug. but where my finger is pointing on the printout is the only thing it could be?

there is pink/black at terminal C and tan/white at terminal A...I dont know.

19795

[dave w]

ok I think it may have been to some sort of fuel module that I dont need? I cant really tell what else it could have gone to. though I will say there is no black/white on the plug. but where my finger is pointing on the printout is the only thing it could be?

there is pink/black at terminal C and tan/white at terminal A...I dont know.

19795

It appears the connector pictured is for an ATC fuse, see link below. Pink wire with a Black stripe is typically ignition "ON". Not sure what the tan/white wire is for.

https://www.amazon.com/Fastronix-Solutions-Fuse-Holder-Parent/dp/B01LWNVT61?th=1

[stackz]

It appears the connector pictured is for an ATC fuse, see link below. Pink wire with a Black stripe is typically ignition "ON". Not sure what the tan/white wire is for.

https://www.amazon.com/Fastronix-Solutions-Fuse-Holder-Parent/dp/B01LWNVT61?th=1

interesting. I wonder if its the 20a in the pic then. most likely I think. gonna probe some stuff later this morning and check it out.

[stackz]

It appears the connector pictured is for an ATC fuse, see link below. Pink wire with a Black stripe is typically ignition "ON". Not sure what the tan/white wire is for.

https://www.amazon.com/Fastronix-Solutions-Fuse-Holder-Parent/dp/B01LWNVT61?th=1

ok, I'm pretty sure its the fuel pump test connector. not sure if it just stays unplugged like this when not in use or not. The tan/white wire traces all the way back to pin B2 on the ecu connectors.

The pink/black stripe wire go over to the oil pressure sender plug. then from the other side of the oil pressure sender plug its the orange wire to the fuel pump relay.

I assume I need to jump this wire or the oil pressure sender wont be doing anything?

[dave w]

The fuel pump relay wiring described above seems odd to me.

Typically, the fuel pump wiring high side gets battery+ from a wire with an inline fusible link or a fuse that eventually is connected to the Battery + terminal.

The computer supplies a battery + signal to the fuel pump relay low side, with the other low side terminal connected to ground. When the fuel pump relay high side contacts close Battery + is sent to the fuel pump.

Typically, the oil pressure switch wiring gets battery+ from a wire with an inline fusible link or a fuse that eventually is connected to the Battery + terminal.

Typically 5 PSI of oil pressure closes the oil pressure switch to send Battery + to the fuel pump.

Typically the oil pressure switch fuel pump wire and fuel pump relay fuel pump wire are spliced together so either the fuel pump relay and / or oil pressure switch will supply Battery + to the fuel pump.

Typically ECM Terminal B2 is spliced into the wire that sends Battery + to the fuel pump.

Possibly the wiring diagram shown below is helpful.

19800

[stackz]

I have that wiring diagram sitting next to me at my desk actually and have the notes from binder planet snipped in under it.

it seems weird to me as well but if it works I'm cool with it. I tried taking some overall pics of it. I put a 20a fuse in the connector we think is the ATC. you can see how it just sorta splices into the main harness in the first pic. In the second pic you can see how the oil pressure switch loops back to the pink/black splice and to the orange power wire to the relay. with the way it loops from the tan/white from the ecu and there is nothing left aside from it on the other side of that splice, it kind of has to stay in place as a fused signal I guess? the piece of the tan/white that you see that is cut went to something else not part of the main engine harness (when I grabbed this harness I just grabbed literally everything under the hood as one big mass). but thats why I think this is the fuel pump test connector maybe?
1980119802

[dave w]

The fuel pump relay actually has 3 high side connectors, that allow for Normally Closed contacts and Normally Open contacts.

The fuel pump power is connected by the Normally Opened contacts.

The fuel pump prime is connected by the Normally Closed contacts.

[stackz]

cool, I will look into more tomorrow. I just finally figured out how to get the pins out of the ecu connector. I'm going to pull them one at a time and unravel this birds nest once and for all so I can lay out all the circuits without them all being twisted up into each other.

I know that will help me better visualize the fuel pump circuit.

[1project2many]

Are you working with a square body R/V harness or the K truck harness? R/V had some different connectors and used some different wire colors.

There are tools to help remove the ecu pins. They are very, very helpful for this work.

[stackz]

K series. Came from a blue 88 truck

[1project2many]

Ahh... Yes, the blue ones are different. ;)

The first year trucks were set up a little differently. The relays weren't all installed on the RH side of the cab in a neat row. The fuse holder is for the fuel pump fuse. It might only have been 15A.

[stackz]

lol, you know what I mean. it wasnt a recreational vehicle is what I meant. it makes sense as one of the wires in the harness is a different color from the chart as well. when I get a chance, I'll go figure out which one.

I plan to head to the upull on friday if the rain holds off to grab some spare connectors and such so I can finish this up and get it on my test stand engine and see if it burns up or not haha

I'm hoping the newest 89 truck that got dropped is complete wiring-wise so I can compare it to this one and get anything I feel I might need...and pics of it all before I cut stuff out. or I may just take the whole harness again...I think its like $30 for an entire harness.

is there 3 or 4 wires that hook to the ALDL, anyone know? my diagram shows 4 with two orange wires connecting in two different places and then joining in the harness. just want to make sure I have that done right.

the wire thats different from the charts for me is pin B7. in the chart i have, it is a black wire and goes to the ESC. on my harness its yellow with red stripe. it does go to the esc connector though so I'm cool. harness also doesnt have pin B8 (dark green for a/c signal) that just tells me the truck probably didnt have factory a/c.

Im pretty sure if i want the ecu to control ac in the future (I plan to put an aftermarket ac setup on the 59 apache eventually) I can just toss a pin in there and wire to the ac clutch positive so the ecu will know its on. I kept the ones I removed from this harness already just in case.

[stackz]

finally had a chance to get back out to the upull and they had a 88 and 89 truck with intact harnesses. yup, the connector was a fuse connector. went ahead and grabbed one plug with the cover and some other bits and pieces to replace some mangled stuff on my harness...as well as spare connectors and such.

19815

[TriumphR3]

Yep, that’s the fuse to the fuel pump. Definitely need that. Looks just like the one on my 88 C1500.