Mystery wires on my HT740

[Iceni John]

While trying to get my Jake working right, I was looking for the transmission lockup wiring that should (theoretically) feed to the Jake relay.   I never did find them, and it seems my Jakes have never had any lockup signal  -  they can be turned on even in Neutral!   However, I did find a large sender on the driver's side (the transmission's "right" side) tail end near the driveshaft, with three small wires coming from it in a white sheath, a red, a white and a black.   They're connected to who-knows-where-or-what?   What are they?   I know they're not for the neutral safety switch, the backup switch or the temperature sender.   All my Allison info and my bus's full schematics don't mention or show anything in this area at all.   Very weird.

And yes, I did check the four ports under the torque converter housing!   All four are capped, with no senders there at all.   That's where I would have expected to find a lockup sender, not at the opposite end near the driveshaft where the mystery switch is.

Anyone here know what these wires are?

Thanks, John  

[luvrbus]

That is a impulse generator for a tachograph or speedometer they are probably running your speedometer from it, it has nothing to do with a lockup,the basic lockup will have a line from the rear test port with a electric/air skinner valve then a line to the torque converter test port If your Jake is engaging in netrual you need to add 2 pressure switches for the early DDEC with a 740    

[Iceni John]

Aha, that makes sense!   Thanks.   It's probably for the VDO tachograph or the Teleflex tachometer  -  the speedometer gets its signal from the right front wheel.   I'll check if the Jake is working in 1st and in 2nd converter:  if it does then I'll know the transmission isn't talking to the Jake at all, and only the DDEC is telling the Jake to operate at No Fuel.   Does this impulse generator run off the rear governor?

Thanks for your help  -  you're the best!
John

[chessie4905]

   It won't be for a tachometer or engine rpms would be reduced by whichever gear transmission was in.