Check, direct hot to grey(pump) wire spins the pump, and I can hear action under the hood ie fuel flow.

But my battery appears to have gone south, weak cranking then click, click. It'* from 10/13 past it'* expiration date, a Napa 75/75.
No further work can be done until a proper battery is acquired me thinks. Electrical work with a weak battery, no.

New Napa 7575, same results, quick flash to the grey wire.
Cheap ignition switch maybe ? it wasn't OEM.

Alright, tell what you think. I'll state facts only.

Installed new battery.
Relay new.
Fuse new.
Pump runs on direct power.
Same flash at connection under the seat.
Three second blast of starting fluid in the intake, fired up for a second, strong cranking.
Retry, three second blast of starting fluid in the intake, click,click,click,crank and fire up again.

Ignition switch and fuel pump switch/oil pressure sensor are the only remaining devices on the circuit.

From fuel pump/inj fuse three pink wires power fuel injectors, pump relay, and the pump/oil pressure switch.I have power to the relay.

I don't like throwing money away, but I'm going to buy an ignition switch, might regret it, might not.
Only pulling the trigger on the buy because of the starter clicking with new battery combined with the fuel pump problem and it was a cheapie switch.
I'd rather buy a new switch than test that 11 pin POS super PITA.

Here'* a diagram I found on-line, I am however working with(wait for it) Haynes, dropped the H-bomb,lol.

Conflicting data on the oil pressure/fuel pump switch.

1. taken from diagrams post.
Hi Jon,

If I may jump in here, yes the oil pressure sender does interrupt the fuel pump to stall the engine. Here is a wiring diagram so you can see exactly how the system works.

Please let me know if you need anything else to get the problem fixed.

Best, Ken

2. Rockauto ACDelco description.
GM Original Equipment The ACDelco GM Original Equipment Fuel Pump and Engine Oil Pressure Indicator Switch is a GM-recommended replacement for your vehicle'* original component. When our vehicle is low on oil, the engine oil pressure indicator switch will light up the corresponding indicator on your instrument panel. In certain applications, the engine oil pressure indicator switch will power up your fuel pump if the fuel pump relay is defective. This original equipment fuel pump and engine oil pressure indicator switch has been manufactured to fit your specific GM vehicle, providing the same performance, durability, and service life you expect from General Motors.

One states it interupts the circuit and the other states it my help power it if the relay goes bad.

Diagram has grey wire coming from oil/fuel switch connecting after relay, so how could it interrupt the circuit that way, appears to me as two power sources for the pump.

From Mike'* thread about OSB 1

GM OBD 1 Paperclip testThis test ONLY applies to GM vehicles with the 12 pin ALDL OBD connector.



To check your computer for stored codes, open up a paper clip and insert one end into the A slot and the other end into the B slot. Be cautious of the orientation of the connector. In some models, its upside down and you would end up using pins G and H.

Now, sit in the drivers seat with a pad and pencil and turn the key to ON or RUN. Do NOT start the car.
The first code should always be 12. This is to tell you that the OBD system is operating correctly. If there are no other codes present, code 12 will repeat itself.

The check engine light will flash for each digit in a code. Take code 12. It will flash ONCE for 1, pause, and TWICE for 2.
FLASH, pause, FLASH FLASH. = 12

If there are 3 codes like 12, 14 and 21 will look like this...
FLASH, pause, FLASH FLASH = 12
Pause
Pause
Flash, pause, FLASH FLASH FLASH FLASH = 14
Pause
Pause
FLASH FLASH, pause, FLASH = 21

When its done with the last code, it will go back to code 12 and repeat.

To clear the codes. Turn the key to OFF, remove the paperclip, and disconnect both battery cables. Wait about 10 minutes and reconnect.

Will this work with my 95' OSB 1.5 ?
I have a 12 pin connector.

In my experience with older cars with fuel pump problems, it'* usually the ground wire.
If you turn the ignition on and the grey wire for the positive side of the pump lights up, you're good.
With the ground being attached to the subframe or body under the car (especially an older and possibly rusted car) the ground might be enough for the initial surge of power, but fails when trying to hold a load.

To eliminate the possibility of a bad ground or even a bad power wire, try going up the wire harness as far as you can to the pump and splicing in a new ground wire and making sure it is connected to a "CLEAN" ground somewhere else. Even if you have to get some sand paper out.

If that fixes your problem, make sure all of your splices are sealed water tight to prevent corrosion in the future.

Regarding the oil pressure sender versus the fuel pump relay:

On many GM starting in the late 80'* near as I can figure, the oil pressure sender supplies power to the fuel pump when enough oil pressure has built up. The fuel pump relay does same thing, just faster. So: If your $10.00 relay goes out while you are driving down Interstate 666 in 90MPH bumper-to-bumper traffic, your engine won't die and you won't die in a fiery crumbled wad of Pontiac. Next time you start your car, it will crank for a long time before firing, because it had to build oil pressure first. Now your complaint to the dealer will be "my car takes a long time to fire" instead of "I died in a ball of fire". This saves GM at least $0.69 on every car in lawsuits.