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Allison HT-741 Wiring
#1
I'm posting this for future reference.

The HT-741 needs to know the throttle position in order to decide how hard to slam together the clutches for the various gears. Below 60% throttle is soft shifts, above that is hard shifts. The engine computer has an output signal that shows the throttle position. That signal has to go through a conversion circuit in order to be used by the transmission ECU. That conversion takes place inside a 2" square black plastic box mounted on the right firewall of the engine compartment. Mine says "KDS Controls" on it. One wire into it is crimp spliced to the wire from the engine DDEC and the three wire black plastic detachable connector goes to the transmission ECU.

The "Check Trans" light will be on whenever the ignition key is on and the engine is off. Once the engine starts, the oil pressure switch mounted on the right rear of the 8V92TA engine allows the ECU to enter its startup test flash of the light. If there are trouble codes detected by the engine, with the engine running you can flip the "Check Trans" switch up and read the trouble codes as flashes of the light. The codes will remain stored in the ECU as long as there is battery power to the ECU (separate source from either the ignition switch or from the oil pressure switch). I'm not sure whether turning off the battery shutoff switch will delete the codes. Unless you have a Allison code reader instrument the standard way of resetting codes is to disconnect battery power.
Jon Kabbe
1993 coach 337 with Civic towed
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#2
It took me a while to figure this all out.

The Allison ECU is mounted in the compartment just ahead of the entry door. It is mounted in the back of the compartment with a vertical stack of five relays and three circuit breakers above the relays.

The relays are assigned functions as follows, starting from the top relay and working down.

Neutral Start - this relay prevents the starter from engaging unless in neutral

Reverse Signal - connects to a relay to control the backup lights and reverse alarm if so equiped.

Check Trans light - this normally closed relay controls the light on the dash.

ECU Power - this relay turns on power to the ECU and Check Trans light when there is engine oil pressure. A wire runs from a circuit breaker above the relays to the rear of the engine to the oil pressure switch and then returns to this relay.

ECU Power - this relay controls power to the ECU based upon ignition switch position
Jon Kabbe
1993 coach 337 with Civic towed
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#3
Thank you Jon, This may prove to be very helpful to your fellow gurus!!!
Especially me since I have a 1993.
1993 Newell 45' 8V92,towing an Imperial open trailer. FMCA#232958 '67 Airstream Overlander 27' '67GTO,'76TransAm,'52Chevy panel, 2000 Corvette "Lingenfelter"modified, '13 Grand Cherokee.
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#4
Nice work, and thank you for posting it for posterity.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )
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