The fuel pump relay is controled by the D-Jet Control Unit, it runs the pump only when 1.the engine is rotating(i.e. running or cranking over) 2.For a few seconds when turning the ignition key off to on. If it's been sitting, cycling the key off on off on will prime it if all pressure has bled out.

Pay attention to the main fuse, if it runs hot, the ends need some corrosion removed and turned in a little tighter.

If you have the correct D jet main relay, there is an internal diode which should block operation of the main relay if the polarity is reversed (i.e. your oops with the battery). This should prevent energization of the D jet under these circumstances and thus prevent damage to the controller. If the relay has been replaced by a generic black cube relay you likely lack the blocking diode and the reverse voltage will have damaged the controller 'if the key was in the run or start position'. If the key was not in the run or start position then the D jet controller should not have been damaged.

With the key in the run position, Eric advised to check for +12v on terminal 87 of the main relay. If you don't have +12v on the 87 terminal, you might have damaged the blocking diode in the main relay with the reversal of potential. That should not happen; but, if it is the cause of your problem count yourself lucky.

The pump relay gets a ground switched control signal from the controller. As noted, terminal 30 on the pump relay should have 12 volts on it all the time. The fuel pump relay coil (terminal 86) gets +12v from the main relay when it is switched on. The other side of the fuel pump relay coil (terminal 85) gets connected to ground in the controller (ground switched) to energize the relay and switch the pump on. Except for the short prime pulse when you first turn the ignition on, the controller will not ground terminal 85 unless the engine is running. As noted by Eric, with the key in the run position if you ground terminal 85 and the pump runs, then that is an indication that you have a problem with the controller or the wiring between the fuel pump relay and the controller.

If you can get into a quiet area, turn the ignition switch to run and standing next to the engine with the hood open, grab the throttle cable connection to the throttle switch and rotate the throttle open and closed. You should be able to hear the injectors clicking open and closed as you rotate the throttle switch. If you don't get any noise from the injectors, then that may be confirmation that your controller is toast. If the injectors click, that does not mean that everything is OK; but, at least the controller is not completely dead.

140 Factory Service Manuals.

https://ozvolvo.org/archive/

The archive contains 1969 and 1974 140 green manual sets.

The sort begins with:

TP10867-1_1974_140_section_0_general.pdf

Sections 0 to Section 8. Download the PDF.

There is the "TP xxxxx 1973 140 Greenbook (incomplete).pdf". That may help.

I'm unsure yet there may be some slight variation between the 1973 and 1974 model year. Eric Planetman knows best.

There may be other archives I've yet to access again.

Questions?

Hope that helps you.
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Hello,

The ECU does control the fuel pump.

Do you have power at the "30" terminals on the fuel pump and ECU main relays?

The main relay 30 terminal should have power all the time. The fuel pump relay only gets power with the key in the On position.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com