re. Cutting out on Highway!-Where to start looking

[Ben Swann]

I'd be checking your ignition switch - MTBF around 130 Kmi.  he fact that it just cuts out indicates it is losing a connection from ignition track 15 (I've got to much Robert Bentley Diagram in my head now).  They get more flaky when they are hot, until one day - nada.

If you don't have the diagram on hand, I just posted some things regarding the wiring that may help. 

You may be having the Fuel pump relay cutout for some reason, but as i have seen the ignition switch fail on these car several times in the ones I've owned, I'd take a SWAG that it is the ignition switch.

It could be the fuel pump, and if yours is failing, I'd expect it to be making some weird noises and drawing more current than normal.  How you check this, i don't know off hand, 'cept you probably need to connect an Ammeter inline.

Also, not to preach, but get yourself a Bentley/Factory service manual.

Ben

[Subject is an '87 5kTQ..... Driving along no strain, not pushing it... 
(only .5-.8 bar) avg speed 70mph, and nothing I could detect with the 
stereo off, when poof no sounds just a stuttering little dip in the nose 
and I could tell the engine was off. It retsarted without hesitation by 
turning key in ignition switch, while I was still cruising with my foot 
on the clutch peddle.... happened 4 or 5 times, but made it home fine 
and there's no problem starting, though the fuel pump has been 
humming... That it?]