To kick this off right, let me give you a little background.
I have a 75 gt 750 it is a very early production 75, according to the frame# from what I could find. Here is the best part the engine on it appears to be and judging by the #s is a 74, I have gone through just about every wiring diagram that I could find. The ones here on line the ones in my 70's era clymer manual and everything else I could find. I am pulling my hair out on this one. some of the wiring matches up to the 860gt diagrams and some matches up to the 750ss diagrams. Now before you jump to conclusions and assume that this was some sort of basket case bike it was not. my dad was the orignal owner on this bike and has only fixed some of the wires that had gone bad over the years. I have been riding the bike for 3 years fixing the issues as the came up, and last year it all came to a head. The Original wiring harness was so spliced and repaired with roadside fixes, and so on and so forth there was barely a section of wire longer than 12". I was tired of getting stranded with a dead battery, or having it die on me in the slightest drizzle, I began to think that I may re wire it over the winter.
It is 5 til june and I am still trying to figure out what is going on with this thing, every time I see I have done something correct to one diagram I find it does not match up with the rest of the bike.
Kinda at my wits end and about ready to give up on trying to figure this out and that really is upsetting more so than the frustration of trying to read italian wiring diagrams.
any advice or tips are welcome.
early 75gt wiring insanity
Your best bet is to rewire it and simplify things as you go.The stock harness was too light a gauge of wire and the switches were horrible.Using heavier gauge wire will improve the headlight brightness and you can wire in relays to eliminate the switches having to handle the high currents the light and horn draw.As for the battery going limp it is a common problem on the 750.The alternator output is just not enough to maintain the charge if it is run at less than 4000rpm with the lights on.The fix is an ST2 alt. rotor or an upgraded one available from I think Road&Race in AUS. Try a search on this site and you will find the info you need.