Another one. I checked the resistances from the TFI module connector through to the connector against the drivers side. All of them are ~0 ohm(closed) except pin #2 on the TFI(see Haynes, if you want).
Ive been noticing almost no difference when adjusting timing on my truck from 10BTC to 20BTC. This leads me to believe its falling back to default. Truck is running like it has no timing control.

Any ideas what this wire exactly is used for?

Its the Green wire with the yellow stripe. I might try to get another harness at a junk yard. Or just replace the wire.

 

is the spout connector installed? Needs to be removed for setting the idle timing but maybe someone forgot to reinstall it after they were done with the timing strobe. Hence a wire open circuit....?

If you've not seen the spout it is a small plug in a socket thats abotu 3" down the loom from the TFI controler box the drivers side wing. Mine is grey. Imagine a big fat 2 blade fuse... (well sort of...)

 

just got the haynes book out the car and althouhg you don't specify which motor you have I don't see a gn-yw wire on or near the tfi module for a 1990.

Maybe you could clarify where you see the detail in the haynes book?

Simon

 

'90 EFI 351W

Well it wasnt really an open circuit. I read Haynes wrong. All the voltages and resitances are fine. I ddint finsih yet though cause my multimeter battery died. Im on the PIP tests in the Haynes manual.

 

ah, fair enough. glad you got it sorted in the end.