1978 wierd ignition switch problems

[sweetgrrl]

hi everyone. i recently picked up a 78 280Z that has, for lack of better words, a nasty electrical gremlin... I've tried replacing the ignition switch, and it didnt help. with the switch in the off position, everything is as it should be. When i move it to the ACC position, i get the dash warning lights and buzzers, the fuel and temp gauge works, and i also get the fuel pump running (well, that is the fuel pump runs only if i unplug the oil pressure sending unit..). When the switch is moved to the On postion, everything goes away except the amp gauge. and when the switch is moved to the start position, the starter cranks like it should, the car gets spark, but the fuel pump is no longer getting power. any ideas would be very helpful and greatly appreciated.

Holly

[sblake01]

Did you replace the key cylinder part of the ignition switch or the electrical part on the back? It sounds like the electrical part could be the problem.

[sweetgrrl]

hi, i replaced the electrical part of the switch.

[sblake01]

The only other time I ever experienced that was on another car when the pin on the back of the cylinder part of the switch was worn or broken so as not to put the electrical part in the right positions when you turn the key.

[sweetgrrl]

ive thought of that too. even with the electrical part of the switch off of the lock cylinder part, and turning the electrical part of the switch with a screwdriver it does the same thing. its wierd. my only thought at this point is that maybe someone who tried to fix the car before me ( as i did buy it in this condition) switched a couple of wires somewhere. well, I'm going back out to beat my head on it some more....

Holly

[2ManyZs]

My question would be if you replaced the electrical part of the switch with a brand new piece or a used one? Does everything else go off along with the fuel pump when you put it in the ON or Start position? If it's just the fuel pump that goes off, it could possibly be the fuel pump relay on the kick panel that is bad.

If the switch you used wasn't new, it may have the same problem the one you replaced had.

MidwestZ has both parts of the switch available brand new, although, the complete switch is a bit pricey.

[sweetgrrl]

the electrical part of the switch was replaced with a known good used one ( out of the 79ZX), and when the switch is in the ON position, everything shuts off..the fuel pump, the gauges, the warning buzzers...the only thing that i know of that stays on is the amp gauge.

[mdbrandy]

Don't know if it'll help, but...

I was just watching a Z-injection video from Z-Therapy yesterday with Kim Bough from Idaho Z-car. Apparently some of the latest '78 280's (and ZX's) used a circuit involving the oil sending unit and the alternator output as a kill switch for the fuel pump. You can tell if the oil sender uses the two spade plugs instead of the single bullet plug. This system replaced the airflow meter kill switch on the earlier FI system. I believe taking the oil sender connector off (and the alternator plug, I think) was the way to test it.

That would at least explain the oil sending unit connection to the problem...

[2ManyZs]

And, if your 280 doesn't have the oil pressure cut off switch, since the switch you used was for a 79, that may the whole problem in itself.

For what it's worth, mixing the different years is never a good idea with electrical parts, there are so many different variations of connectors and shared systems in the electrical system that it usually won't work. It becomes even worse with the fuel injected cars.

[sweetgrrl]

both ignition switches have the same part number, so they would be interchangable. even when i dont use the switch, and jump the connector with jumper wires, i still get the same result.

Holly

[2ManyZs]

If they've got the same part number, I guess that shoots that idea out the window......

I'd be looking at the tumbler portion of the switch, ignition relay in the engine compartment on the bracket in front of the battery, fuel pump relay( think that's on the kick panel under the glove box) and even the fusible links under the hood as the next possible causes.

[sblake01]

The ignition relay on a 78 is in the bracket in the kick panel on the passenger side.