I had my 1989 my XJS V12 out for a drive yesterday and was a stop light. When the light changed i had no power and it would not turn over. About a half hour later it started back up. I am sure it was a vapor lock. What can I do to prevent this from happening again; Thanks

 

Does the air conditioning work? There’s a heat exchanger that uses the ac circuit to cool the fuel. Is that all still there and functioning?

 

The air works great but i did not have it on at the time

 

When you say "it wouldn't turn over", that generally means it wouldn't crank. Is that the case, or do you mean it would crank, but not start?
Jon

 

It would not turn over . no cranking

 

So this just died at a light and wouldn’t restart? Was there sputtering or rough running before it died or was it like you just turned it off?

it’s sounding more like an electrical issue than a fuel issue to me.

 

Sounds like a starter issue, since it apparently didn't engage. Several things in that circuit, ignition switch, starter relay, solenoid, starter itself. Neutral safety switch, poor battery ground, poor engine to chassis ground.
Assuming you put the car back into park after the engine stalled, exactly what happened when you turned the key to off, then to start? Dash warning lights come on, relays clicking, stuttering at the starter?

 

Vapor lock can only occur , on the inlet side of the fuel pump (usually engine mounted mechanical pump), and which is caused by a clogged/restricted fuel inlet. Typical problem on flathead Fords with the fuel pump mounted up high on the motor.

Not so much on anything since then.

It has nothing to do with engine cranking.

Doug