OK, yeah I know I should just get an MBC, but I have this Turbo+ kit from my original 88 740T (LH2.2)…and now installing it in the 91 240 B230FT project. Pic below is from the LH2.2 Turbo+ installation manual. I'm trying to figure out if I need to hook up the control unit terminal 2 (red/white) wire to anything. It seems have gone to a test port on the original 740 LH2.2 harness, but I'm unsure whether that somehow sent or received a signal of some sort to/from the Turbo+ control unit. Anyone have a wiring diagram for the later LH2.4 Turbo+ system?

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It looks like it is only used for some kind of diagnostic purpose, I imagine you can ignore it. Does the manual talk about how to run diagnostics on the control unit? That might add useful context.

^^ That's a slightly different diagram to the one in the '29145' Turbo+ guide from the Tech Archive.

Unfortunately, the '29145' guide appears to be designed by the "Fitting Turbo+ For Dummies" publishers and there's precious little (i,e. nil) info about what the wires actually do, or where they go to, beyond the t+ kit.

The only red-white wire I could find in in the TP31058_1 1987 740 760 Wiring Diagrams PDF (in the Tech Archives) on p.16 or PDF page 18, is the red-white wire going to pin 12 of the LH 2.2 ECU.

It's marked [220] on that diagram, as the 'test point CIS system'. The arrow on the drawing suggests it's an output from the ECU, but without knowing what pin 12 of the ECU does, exactly....

    Major Ledfoot Yep I think you've come to pretty much the same conclusion as I have…and as per @jamesinc 's comment, I think I'll just leave it disconnected for the time being. I'm a bit peeved at myself as I mounted the T+ control unit etc. and went to run the harness over to the battery and coil only to find the coil wires don't reach regardless of how I run the harness (unless I want to run it straight across behind the radiator fan LOL) Grrr! So, I'll have to extend them. Might as well tidy up the length of some of the other wires while I'm at it and as some are way too long, given the harness was set up for a 740T.

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