Fuel Pumps won't prime
 

(tl;dr question at the bottom)

Hello,

'99 Trans Am. Heavily modified (f1x/427) running dual fuel pumps.
The car has been sitting for a long time.

I recently tried to start it - and realized my pumps will no longer prime. Rest of the car gets power, all lights on, etc. sitting at 12-ish volts.
I was previously running a single pump harness. So I figured perhaps it went bad an I took this opportunity to upgrade to a proper dual pump harness.

Running the following harness now:

https://www.racetronix.biz/p/udp-hd-...mp280/udph-005
With the intermediate all connected up, etc.

Using a continuity tester, I am getting the tester to light up on both ATM Fuse containers, on both wires. So power is there.
However, my HIH (hobbs) are both just hanging there, as I don't currently have a hobbs pressure switch (so both pumps would be running? and this is where the question comes below):

tl;dr:

Does this harness *require* the HIH Inputs to be jumped? Or can they just hang there and the fuel pumps should both work?
Could both of my fuel pumps have simply died?

Thanks,
Andy

Also, I did a continuity test at the intermediate harness. Only the purple (signal?) wire lights up - the others are do not. I figured the hotwire should as well? this is not my area of expertise, just an area I am familiar enough with to replace the harness.

https://cimg3.ibsrv.net/gimg/ls1tech...adb639891f.jpg

UPDATE: 4/11/2023:

Raising this thread back from the dead: I never did resolve this, unfortunately.
Updates:

1) I rechecked the following grounds

• Redundant relay chassis ground (under the passenger driver side)
• Front ground that goes to chassis near the double fuses
• Rear ground by the gas tank supplied with the intermediate harness

2) I used a tester to test for power and signal:

• I get power on both the Big blue and Big red wires to the pump that connects to the bulkhead connector
• I get power on the gray colored wire for 3 seconds (upon key on) on the 4 pin square connector (I presume this is signal?)
• I manually power the pumps and they spin using a 9 volt battery

3) With all grounds checked, and power going exactly where it should, and verified pumps are working, why in the world would my pumps still not prime?

What am I missing?

Each pump has it own wire harness. The fuse in each harness completes the circuit for each pump (on my harness each one terminates in the engine bay).. The blue harness for one pump, The red harness for the second pump.
If you want to run a single pump insert the fuse in either the blue or red hanress or in each harness if you want to run two pumps.

When you get a hobbs switch, a short harness runs to the hobbs switch. At 4 psi for instance, the hobbs switch completes the circuit for the second pump.

It is usually this ground that becomes corroded. You must disconnect and grind down to bare metal. Apply dielectric grease and reconnect it.

I will inspect the grounds. Thank you for your help!! and the pictures

I had nothing but problems with that harness, well basically all their wiring. Had to pull it all out and just wire it up myself

Raising this thread back from the dead: I never did resolve this, unfortunately.
Updates:

1) I rechecked the following grounds

• Redundant relay chassis ground (under the passenger driver side)
• Front ground that goes to chassis near the double fuses
• Rear ground by the gas tank supplied with the intermediate harness

2) I used a tester to test for power and signal:

• I get power on both the Big blue and Big red wires to the pump that connects to the bulkhead connector
• I get power on the gray colored wire for 3 seconds (upon key on) on the 4 pin square connector (I presume this is signal?)
• I manually power the pumps and they spin using a 9 volt battery

3) With all grounds checked, and power going exactly where it should, and verified pumps are working, why in the world would my pumps still not prime?

What am I missing?

Issue resolved...................Problem: Not remembering that 4 years ago when I originally upgraded to dual pump while running on a single relay system (under-spec'd) I used a series circuit. I switched to parallel circuit in the in-tank harness, and voila...

Absolutely great to know!