Need inspiration on electrical issue

[Tedtiler]

Weird electrical issue.  Car will not crank . Fuel pump no noise. Battery good all fuses and relays good, earths good. Immobiliser light goes out ok. Oil pressure light will not light with ignition on either.

I can replicate the oil pressure light not lighting in my other mr2 by unplugging the ecu completely but even then it will still crank engine with ecu unplugged.

Changed over ecu in between cars, no difference.

I can make the car crank by appying power at the starter relay .

If any of these symptoms rings a bell please post. The oil pressure light/no fuel pump noise thing leads me to think its more than just a dodgy starter feed. Im stumped..

[Carolyn]

Sounds like it could be the ignition switch itself.

[jonbill]

When you put the key in and turn it, do all the other dash test lights lightup? Only oil pressure doesn't?

[Topdownman]

Years ago I had a scenario where the headlights came on but the car wouldnt turn over.

It turned out to be oxidation on the battery terminals making a poor circuit that was good enough for the lights but not good enough for the higher draw of the starter. May be worth taking off the terminals and sanding them and the inside of the clamps to make sure the connection is good?

Will only take a few minutes and nice to discount something simple?

[Tedtiler]

Yes all other dash lights come on. Battery is new and terminals fine. Car was working fine . Crank/fuel pump seems to be systems that work  independently of ecu .

As i said i can crank the engine from the starter relay pins.  Something has decided not to send a signal, fuel pump too

[Carolyn]

Sounds, then as though the problem is in the main ignition circuit.  Are you SURE the relay is good?  I'm afraid these problems are a tedious process of elimination. Very hard to help by remote!

[Tedtiler]

Sure is a headmelter especially without seeing the car. I've changed all the relays twice. Was hoping someone had experienced a similar thing. I'll keep looking. Thanks for the reply's folks

[edmundopt]

There's a starter relay and a ignition relay

IG1 is located under the dash near the drivers door
ST is located near the battery

[Carolyn]

I'm still thinking ignition switch, as some cars have two circuits going from the switch.  Not sure in the case of the Roadster, But I'd get a meter on the back of the switch and see what gives.

[shnazzle]

I'm with Carolyn. Fuel and starter are not connected so if both aren't kicking in, have to look at the top of the food chain...ignition switch. Especially if you can make it crank at the relay.
It's not receiving the signal to kick the starter and push fuel

[Carolyn]

Also, I am now dimly recalling a similar problem, but on a different car (which matters not).
The switch tested fine, but it was not operating the relay.  Turned out it was a broken wire, in the ignition switch harness.  This can be tested at the relay, by seeing if the coil side of the relay is getting volts.

[Tedtiler]

Cheers folks I'll try that tomorrow. Really appreciate your help.
Raymond