Help with fuel pump wiring?

[Mike5442]

Hello,
I have recently acquired a beautiful 1982 DeLorean with about 16k on it. Unfortunately the previous owner let it sit too long so it needs fuel system work including a new pump etc.....

I opened the access to the fuel pump (the rubber pump cap was missing) and came across a taped up splice on the pump leads, one was grounded to the frame, and I followed the other black wire back to the battery box onto a relay?. It doesn't look very professional to me and I'm not sure what it's function is.

Can anybody identify this relay or have any ideas as to why it is spliced into my fuel pump circuit?? I've attached 2 pictures.2914729146

Thank you!!!!

-Mike

[STAINLS]

Hello,
I have recently acquired a beautiful 1982 DeLorean with about 16k on it. Unfortunately the previous owner let it sit too long so it needs fuel system work including a new pump etc.....

I opened the access to the fuel pump (the rubber pump cap was missing) and came across a taped up splice on the pump leads, one was grounded to the frame, and I followed the other black wire back to the battery box onto a relay?. It doesn't look very professional to me and I'm not sure what it's function is.

Can anybody identify this relay or have any ideas as to why it is spliced into my fuel pump circuit?? I've attached 2 pictures.2914729146

Thank you!!!!

-Mike

Mike, you are 2 vins away from my first DeLorean. Welcome to the forums!

[STAINLS]

Assuming the number in your user name is a vin reference.

[Bitsyncmaster]

That PO fix was probably because another component or connection failed. The RPM relay should power the pump and those do fail often. The inertia switch is what grounds the pump and those can fail. The connectors (that two pin one by the pump) also fails quite often. There are more connectors up by the washer bottle but those don't fail as much.

[DMCMW Dave]

That PO fix was probably because another component or connection failed. The RPM relay should power the pump and those do fail often. The inertia switch is what grounds the pump and those can fail. The connectors (that two pin one by the pump) also fails quite often. There are more connectors up by the washer bottle but those don't fail as much.

I agree - looks like a haywired replacement for a bad RPM relay by someone who didn't understand the circuit.

[Jonathan]

Mike,

Have a look through your fuse and relay area above the battery area and accessed by removing the parcel shelf board in that corner behind the passenger seat. Compare what you see there to what you see on this schematic and report back the differences.

Generally, the best thing for the long term health of the car (and you) would be to try to return it to it's originally intended wiring design. You can make changes as per the upgrades or recalls in some cases, but getting back to stock early on in your ownership will make your life easier in the end with this car.

Welcome aboard!

29154

(This file and many others are also in the Resources section. This one got revised to make it clearer I think, but the content stayed the same).

[Mike5442]

Assuming the number in your user name is a vin reference.

No sorry I didn't even think of that when I made my name! lol but Thanks! my VIN is 10268

[Mike5442]

Mike,

Have a look through your fuse and relay area above the battery area and accessed by removing the parcel shelf board in that corner behind the passenger seat. Compare what you see there to what you see on this schematic and report back the differences.

Generally, the best thing for the long term health of the car (and you) would be to try to return it to it's originally intended wiring design. You can make changes as per the upgrades or recalls in some cases, but getting back to stock early on in your ownership will make your life easier in the end with this car.

Welcome aboard!

29154

(This file and many others are also in the Resources section. This one got revised to make it clearer I think, but the content stayed the same).

As yes absolutely! I am an electrician by trade so messy wiring is a big pet peeve of mine lol. I am in the process of assembling a parts order (including the updated fuel pump setup and manuals) but I wanted to clarify what looks like a hack job first.

In the picture I posted of the relay in the battery compartment, the red wire coming off this rogue relay goes up into the fuse area but I will have to trace it further. So my assumption that this relay doesn't belong there is correct I take it?

I do want to add when I crank the engine I do get voltage at the connector (made me wonder why something was spliced into the circuit)

But anyways, thanks for the info so far. When I get a chance I will report back my findings!!

-Mike

[Rich]

Have a look through your fuse and relay area above the battery area and accessed by removing the parcel shelf board in that corner behind the passenger seat. Compare what you see there to what you see on this schematic and report back the differences.
Generally, the best thing for the long term health of the car (and you) would be to try to return it to it's originally intended wiring design. You can make changes as per the upgrades or recalls in some cases, but getting back to stock early on in your ownership will make your life easier in the end with this car.


+1

You do want to get back to the OE component and wiring arrangement. The RPM relay - that seems to have been bypassed or tossed - provides a safety interlock such that if the engine stops turning then a second later the fuel pump voltage is switched off. It also keeps the pump from running continuously if you move the key to ON and decide not to crank the engine. The RPM relay can cause problems of its own as others note, problems readily solved by sorting out its connection or replacing it. Carrying a spare isn't a bad idea when you are done putting the wiring back in shape.

[Mike5442]

Alright I traced the wires coming off this mystery relay:

(Terminal numbers are in the picture of the relay)
The black wire off terminal #85 goes to ground.
The white wire off terminal #86 went up under the dash but is cut and not attached to anything (anymore at least)
The yellow wire off terminal #87 splices on to a black wire and runs to the fuel pump.
The red wire off terminal #30 runs up into the fuse box area and attaches to the "Door Lock Breaker" (#36 on the fuse layout picture above).

Apparently this relay must do nothing anymore as terminal #86 is cut, so the relay cannot close anymore. (I'm not sure what kind of switch was used up near the dash to close the relay but it isn't there anymore)

My question is: So when is the "Door Lock Breaker" powered or what is the function of it? In other words; why would someone grab power from the "door lock breaker" to run the fuel pump?; Does it sound like something that would have been done to bypass the inertia switch and/or RPM relay?

I've attached a picture of the fuse box area and the mystery relay. In the picture of the fuse area, the red wire cutting across the "Door lock module" onto the "door lock breaker" is the red wire coming off the mystery relay.

Maybe I'll just wait until the new pump arrives and a get everything ready to start her up and find out for sure. Thanks!

-Mike

2919629197

[Jonathan]

That's a good start, Mike.

For the door lock breaker thought, could you perhaps take a photo of under the driver's footwell and show us how your inertia switch looks? It will be the little black box with plunger on top and wiring connector on the bottom. Perhaps mounted to the bracket beside the lambda/service counter, or perhaps to the side on the left attached to the fiberglass. It would normally tie into the fuel pump to shut off power if your car is in a crash.

Also perhaps please take another photo of your fuse relay area letting us see down a little behind that lip of carpet to the first row of relays and also remove the fuse box cover to see underneath.

[Rich]

Apparently this relay must do nothing anymore as terminal #86 is cut, so the relay cannot close anymore. (I'm not sure what kind of switch was used up near the dash to close the relay but it isn't there anymore)

My question is: So when is the "Door Lock Breaker" powered or what is the function of it? In other words; why would someone grab power from the "door lock breaker" to run the fuel pump?; Does it sound like something that would have been done to bypass the inertia switch and/or RPM relay?

To answer this question we look at the functions around the fuel pump. The inertia switch is in the FP ground circuit. The inertia switch is also wired to the door lock module but the lock module isn't telling the pump to do anything. If the car trips the inertia switch then the FP stops running (no ground) and the doors unlock, both functions being for crash safety. Seems as if the hack job may have been done to try to duplicate some of the OE functions. No idea why it needed to be done to begin with, though. Maybe the inertia switch went bad at one point and this was their workaround. You are on the right track trying to put it these circuits back to factory specs. If the inertia switch, terminals and associated grounds are OK then things work fine in factory mode.

General comment since you are digging into questionable wiring as a new owner.
The info you want to review any of your wiring can be found in 3 places:

1. The color wiring diagram in the Resources section of this forum (stickies)
2. The All Wiring Schematics thread in the Resources section (stickies)
3. The Workshop Manual (it has pages that explain how things are supposed to operate), also in Resources - and DMCH sells hardcopies of it

[vps3922]

Alright I traced the wires coming off this mystery relay:

(Terminal numbers are in the picture of the relay)
The black wire off terminal #85 goes to ground.
The white wire off terminal #86 went up under the dash but is cut and not attached to anything (anymore at least)
The yellow wire off terminal #87 splices on to a black wire and runs to the fuel pump.
The red wire off terminal #30 runs up into the fuse box area and attaches to the "Door Lock Breaker" (#36 on the fuse layout picture above).

Apparently this relay must do nothing anymore as terminal #86 is cut, so the relay cannot close anymore. (I'm not sure what kind of switch was used up near the dash to close the relay but it isn't there anymore)

My question is: So when is the "Door Lock Breaker" powered or what is the function of it? In other words; why would someone grab power from the "door lock breaker" to run the fuel pump?; Does it sound like something that would have been done to bypass the inertia switch and/or RPM relay?

I've attached a picture of the fuse box area and the mystery relay. In the picture of the fuse area, the red wire cutting across the "Door lock module" onto the "door lock breaker" is the red wire coming off the mystery relay.

Maybe I'll just wait until the new pump arrives and a get everything ready to start her up and find out for sure. Thanks!

-Mike

2919629197

Hmm, I want to add my 2 cents here.

It sounds to me like the PO was trying (if a switch would be connected to the cut cable) to do a switchable bridge to get the fuel pump running in case the RPM relay would go (like bridging pins 30 and 87 on the relay connector to get home) OR if the inertia switch was tripped (hence the connection to the door lock. I had an issue in my car where the central locking would unlock but not lock. We traced the whole wiring until we found out that the inertia switch had melted. We replaced it and applied the inertia recall to move it to a new location and all is fine with my locking system now.

[Mike5442]

That's a good start, Mike.

For the door lock breaker thought, could you perhaps take a photo of under the driver's footwell and show us how your inertia switch looks? It will be the little black box with plunger on top and wiring connector on the bottom. Perhaps mounted to the bracket beside the lambda/service counter, or perhaps to the side on the left attached to the fiberglass. It would normally tie into the fuel pump to shut off power if your car is in a crash.

Also perhaps please take another photo of your fuse relay area letting us see down a little behind that lip of carpet to the first row of relays and also remove the fuse box cover to see underneath.

Hello everyone, sorry for coming back to this so late, I thought nobody was responding to my thread anymore but I just realized there was a page 2!! (I feel like a dummy now lol) I will get some pictures to see what you think. It will be a little while before I can try starting it up because as a lot of you know, one thing leads to another when working on a car(A lot of "while I am here I might as well do this"). Thanks!

-Mike