So I had everything working well on my carb conversion with the exception of the fuel pump which constantly ran unless I pulled the ground wire per SirAndys carb conversion write up.

Now my pump will not work at all. I direct wired it to the battery to see if the pump was good and it worked. I connected a 12 volt wire to my relay board at the black/red wire #13 connection and it worked. So no issue with the wire. However something on the relay board or relay prevents it from working when the key is turned on.

I was going to wire it to the 2 other points on the relay board to get 12 volts (T4b and the #12 pin on the T12 connector). However, with the key turned on, I am not getting 12 volts to either of these. the T4b, I am getting 2 volts and the pin 12 on the T12 I am getting 4 volts.

My only other option to get 12 volt power is to connect to my coil but I have read this is not a good idea.

Looking for some guidance.

With the key in the on position, do you have 12v at the ends of the pump leads? Running the pump off the coil is a bad idea. Post a picture of the relay board as it is currently configured. When you connected the pump to the battery, was that with 2 wires separate from the harness?

I have ZERO volts to those wires and also Zero volts at the Pin 13. The only thing different from stock is the ground to enable fuel pump relay connected to the car body.

Which ground did you pull? Are you talking about the one that's labeled "Ground To Enable Fuel Pump Relay" in that picture? I'm not familiar with the carb conversion write up.

Yes. That ground is connected to my car body. When I run a lead from the positive side of my battery using that ground, my pump will run when I connect it to the Black/Red fuel pump wire.

I am not seeing any blown fuses under the dash or on the relay board. Is there a set of fuses elsewhere I am not finding. Google search showed nothing.

the last sentence has me confused. The stand alone(?) wire from the bat connects to what? The pump?

I ran just an extra wire directly from the positive battery post to my fuel pump wire that connects to pin 13 and my fuel pump works. I used it just to test my fuel pump if it was working. I think that is what my have confused you and I wasn't clear with that.

It is like I am no longer getting power to my relay plate. I'm not getting 12 volts anywhere on it with the key off or on. My fuse on my relay plate is good.

Click to view attachment

with the extra wire for power and the jumper ground wire grounded to chassis the pump runs, yes?

Yes. So I know my fuel pump is good. It does pump gas when I direct wire it. But I get nothing when I go through the 12v pin points on the relay plate.

It worked fine yesterday through the relay board and then didn't.

This is for the 73 relay plate so it might not be completely accurate for your '72, but it's the best I can work off of, if this doesn't apply AT ALL to your application then ignore this!

You should have power going to the Relay Plate from 4 sources:

2 from the battery all the time (Terminals 12 and 14 on the upper connector, red wires)
1 from the key switch when it's in the On position powering the supply side of Fuse 9 on the under-dash relay (Terminal 8 on the upper connector, black wire)
1 from the key switch when starting (Terminal 1 on the connector, yellow wire) but this one can be ignored for right now.



In order to get power to the fuel pump working you need the Power Supply relay, the Fuel Pump relay, the 2 battery cables at terminals 12 and 14, the 25 amp fuse, power from the key switch/Fuse 9 at terminal 8, and a chassis ground at terminal 10.

Basically the key switch sends power to the coil of the Power Supply relay.
The power supply relay turns on, and takes the battery power from Terminal 12 and sends that power to the coil of the fuel pump relay.
The fuel pump relay's coil is switched from the negative side at the "Ground To Enable Fuel Pump Relay" which is usually a job done by the ECU when fuel injected.
When all of the above conditions are satisfied, the Fuel Pump relay turns on, and power from Terminal 14 goes through the 25 amp fuse, through the Fuel Pump relay, and back to Terminal 13, and finally to the fuel pump through the Red/Black wire.

This is just the fuel injected operation of the fuel pump, what exactly does the guide tell you to do to change it for carbs?

Did you check the pump and power supply relays,reason I ask is I had this issue the pump relay went south,fixed that and then the supply relay did the same..old parts,lucky I have heaps of spare relays .

Are you sure the relay is good? Plug it in to a relay plug for a headlight. If the light doesn't raise, no good. Cleaned the fuse and holders? Corrosion in the relay pin holes? Check the V at the pump end of the supply harness to the chassis. As the pump runs with the direct from bat wire you know andy's trick is doing the job. Points to a power supply issue. The FP harness is suspect. Have you ever removed and cleaned the relay board? Really simple task.

I would suggest getting rid all jumpers, grounds and any other added wiring and run a fused wire from the last resort position in your first post to the pump. if the pump works when switched on with key, your wiring was suspect, if it does not, you have an issue with relay board or before it. I have been running this way for years without issue. the wiring for the pump is simple, switched 12v to + side of pump. - side goes to a chassis ground.

I swapped the relays around but there was no difference. I do have power getting to the relay plate but not working at specific locations it should be after that. I located 2 pins on the T14 connector that work when the key is on and turn off when the key is off. I think one is to the starter or alternator light plug based based on the 73 relay board picture LieroFox posted above. I am going to direct wire to that lead and see how that goes and post back.

Well done!

Yes, the other ones that comes on with key on is the alternator warning light at Pin 2 (the blue wire) and the back-up lights at Pins 3 and 4 (gray/brown wires)... which I forget which one provides power for that one. I believe it's Pin 3 that provides power, and Pin 4 that goes to the reverse lights.

Thanks for this image and info. I haven't seen one like it that details the relay board and wires so easily. Adding it to files!

You're welcome, it's actually an image I found and spent a few hours in Photoshop going through and redoing all the wording for the pin terminals and the relay terminals because the original text was almost completely unreadable.

See also: https://www.youtube.com/watch?v=QEzhxP-pdos

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Not sure but appears you have a bad relay board,if you can't wire as per the tech article you have issues.I know this as mine was DOA,I ended wiring thru the heater boost fan with a 7.5amp fuse till I got a rebuilt relay board...night and day really,just saying

She now purrs like a kitten. Thank all of you for your help!!!!!

What was the fix?

I do not know exactly why the fuel pump wire was not activating at the relay board. So I pulled the red/black wire from the plug, stripped it down and put a jumper lead with a round clip. I then picked one of the 2 pins on that plug that turned off and on with the key, placed the clip on it, pushed the plug back on. Now whenever my key is turned on, my pump works and when key is off, it goes off. Simple fix.

The biggest point of caution I'd give for that solution:

Your fuel pump is now no longer fed by a relay, and the wires coming from the key switch to feed the relay board might cause problems as a result, both from the long path and the fact that they're powering the pump directly instead of switching a small relay coil, depending on the fuel pump you're using that could be between 5-15 amps.

The wire for your fuel pump is also no longer fuse protected, where previously it was protected by the 25a fuse, now there's just a wire going directly from the battery, forward to the ignition switch, over to the un-fused side of the fuse panel, back to the rear again, and finally back to the fuel pump.

I thought about that fuse issue. It was a concern. I am going to add a inline fuse in that wire. I just wanted to make sure it would run well first then do it.

I understand the hack to get by. I do that too. But it is TEMPORARY. Don't just skate by on this "solution" please. If you do every fix like this, your car will be a nasty mess devaluating by the second.

I'm not sure if it's too late now to swap it back to stock or not, but, I'd want to look through the relay board, personally. See where the power is getting lost. Is it getting lost at the Power Supply relay coil? Is it getting lost a the output of the power supply relay? Is it getting lost at the fuel pump relay coil? Is it getting lost at the outlet of the fuel pump relay?

You said in the very first post that there was no power on the switched 12v terminal on the T4B connector, well that 12v comes from the Power Supply relay, so either:

A: +12v key voltage isn't reaching the Power Supply relay (terminal 85)
B: The Power Supply Relay has no ground at the coil (terminal 86)
C: The Power Supply Relay has no power going to its input terminal (terminal 30)
D: The Power Supply Relay has no power coming out of its output terminal (Terminal 87)
E: The Power Supply Relay is just inoperative.

To test the board I'd use a multimeter and test for continuity:
Between Pin 8 on the T14 connector and Terminal 85 on the Power Supply Relay.
Between Pin 10 on the T14 connector and Terminal 86 on the Power Supply Relay.
Between Pin 12 on the T14 connector and Terminal 30 on the Power Supply Relay.
Between Terminal 87 on the Power Supply Relay and Terminal 85 on the Fuel Pump Relay.
Between Terminal 87 on the Power Supply Relay and Terminal 1 on the T4B connector (the top right one labeled Last Resort Unfused Private Switched +12v)

All of those points should have continuity even with the relay board fully unplugged. If all of those test good, I'd test the Power Supply Relay, you could even pull a relay from the headlight motors and swap it in place to test it that way.