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Starter Engage Circuit Wiring

by Barry and Cindy 1997 U270 36'

 Start battery cable connections      

1   Start battery positive post      

2   Starter solenoid terminal   

3   to boost solenoid terminal   

4   Isolator terminal

5   to 90 amp circuit breaker terminal (behind white bay wall panel)
         
   30 amp Allison circuit breaker  (behind white bay wall panel)      

6   input B69   

7   output C6 red   
         
   10 amp Allison circuit breaker #1 (right-dash panel)      

8  input  ATEC-ECM C6 red   

9  output ATEC-ECM 136 white   
         
   Allison transmission ECM (behind lower left driver seat side kick panel      

10  inputs  B2-136A  &  B11-136C -  unswitched battery +   

11  output A23-123 PU Violet - neutral-start output when trans in neutral (closes relay #1 coil)   
         
   Ignition switch      

12  input  91 white from 15 amp circuit breaker #28 (located on front dash breaker panel start batt buss)   

13  output 122 white start position to neutral safety relay common   
         
   Neutral safety bosch relay R1  (right side of front dash CB panel)      

14  relay 86 coil from step#11 (trans neutral closes relay)  123 purple   

15  relay 85 coil (battery negative connected to other coil terminal)   

16  relay 30 common is from ignition switch start position  122 white step#13 (or from remote start button E23)   

17 relay 87 N/O is E9 white to aux start solenoid coil (powered from ignition switch start)  on isolator panel   
          (aux start sol below closes when when trans in neutral & ign key in start position)   
          (and aux start solenoid coil is powered from ignition key start position)   
         
   Auxilary start solenoid  (located on inverter panel)      

18  coil small wire from step#17 (battery positive closes relay)   

19  input large side post from start battery positive step#4  B26 red   

20  output large side post to starter solenoid coil B25 red 

 

START BATTERY      

B1 000 - start battery POS post big cable goes to starter solenoid large terminal

B5 000 - start battery NEG post new very big cable bolted to motorhome frame [change to bolt to engine]
      

View #2 of Starter Circuits

The NS switch is a neutral start relay on our coach.  When we had a start problem, I put lights on the relay coil and points to observe a fast flow of current when the ignition key was turned to start position.

From the circuit description, you will see a dedicated circuit breaker behind the white bay breaker panel the flows start battery current directly to Allison through another breaker by the front door panel.  I replaced both breakers to be sure they were not intermittent. Allison flows current to neutral start relay coil, to close relay points when ignition is on and transmission is in neutral.  The ignition key start position flows current through close relay points to the aux start solenoid that you manually tripped to run starter.

STARTER      

B5 000 - big cable from battery to starter solenoid large terminal

B14 2RD - big cable on start solenoid goes to rightmost isolator terminal
      

ISOLATOR      

B14 2RD -  big cable from starter solenoid

B15 2RD - large cable to 90-amp circuit breaker on bay wall panel

B26 RD - wire to aux start solenoid on isolator panel aux start solenoid
      

BAY WALL PANEL BREAKER      

B15 2RD - large cable from isolator to leftmost 90-amp big round start battery circuit breaker's lower terminal

B69 - wire from 90-amp breaker to 30-amp ATEC circuit breaker on bay wall panel

C6 RD - 10-gauge wire from 30-amp ATEC breaker to front door panel
      

FRONT DOOR PANEL BREAKER      

C6 RD - wire from bay wall panel to leftmost 10-amp ATEC-ECM circuit breaker located on top-row

136 WH - wire from 10-amp breaker to Allison ECM interface-plug RD# 136A & 136C, "unswitched batt +"
      

ALLISON ECM COMPUTER      

ECM computer is located behind carpeted side panel to the left of driver's left foot
   136 WH   wire from 10-amp breaker to both terminals RD# 136A & 136C, labeled "unswitched batt +"

123 PU   wire from ECM terminal PU# 123, labeled "neutral safety", indicating transmission is in neutral, to neutral safety relay
      

FRONT DOOR PANEL RELAY      

123 PU - 12-volt positive from Allison, when transmission is in neutral will close #86 coil on neutral safety relay

Green ground wire completes #85 coil circuit on neutral safety relay located 2nd from bottom on right side of panel

122 WH - ignition key momentary start position flows start battery current to neutral start relay #30 common terminal

E9 WH - ignition key current flows from N/O #87 relay terminal to aux start solenoid located on isolator panel
      

ISOLATOR PANEL SOLENOID

AUX START solenoid is leftmost of the two solenoids and is located in center of isolator panel above air cleaner

E9 WH - ignition key current flows through neutral start relay to small coil terminal on the aux start solenoid, coil is internally grounded to case

B26 RD - start battery current flows from isolator terminal through aux start solenoid when solenoid is closed (by ignition momentary start)

B25 RD - when aux start solenoid is closed start battery current flow to starter solenoid coil to activate engine starter, coil is internally grounded
      

IGNITION RELAYS      

IGNITION DUAL-RELAYS are large cube-shaped and are mounted to lower center of front door panel

REMOTE STOP RELAY is positioned lying loose in bottom center of front door panel

103 WH - when ignition key is turned on, 103 WH flows start battery current through secure-switch to remote-stop relay #30 common terminal and through NORMALLY-CLOSED #87A terminal

103A WH - to dual-ignition-solenoid coils to close ignition relays, which allows start battery current to flow to ALL ignition circuits
      

REAR ENGINE REMOTE START PANEL      

E21 WH   ignition circuit breaker #19 located in front door panel powers remote start system start & stop momentary push button switches

E23 WH   pushing remote start switch powers ignition key start wire E22-WH to turn starter on (same as turning ignition key to start positon)

E61 WH   pushing remote stop switch powers remote stop relay #86 coil, opening relay and turning 103A-WH power off to ignition dual-relays

Green ground wire completes #85 coil circuit on remote stop relay

When remote stop relay is powered, 103A-WH power from ignition key is disrupted, turning off ALL ignition circuits MOMENTARILY, which kills power to engine fuel shut-off solenoid, thus stopping engine letting up on remote stop switch allows ignition dual-relays to again close, as ignition key is still on

View #2 answers your question the NS switch is a neutral start relay on our coach.  When we had a start problem, I put lights on the relay coil and points to observe a fast flow of current when the ignition key was turned to start position.

From the circuit description, you will see a dedicated circuit breaker behind the white bay breaker panel the flows start battery current directly to Allison through another breaker by the front door panel.  I replaced both breakers to be sure they were not intermittent. Allison flows current to neutral start relay coil, to close relay points when ignition is on and transmission is in neutral.  The ignition key start position flows current through close relay points to the aux start solenoid that you manually tripped to run starter.

Our starting problem was a hesitation after turning ignition key to start position.
After a short pause, which made us think it would not start, the engine would start.

The names of our wiring diagrams I used to trace our starter circuit:

B-2126 Automotive Wiring Diagram

A-5894 ATEC Interface Diagram

A-4752 Remote Start Wiring Diagram

B-2198 12V Wiring Diagram

Troubleshooting

First thing I would do, with ignition key off, is to put 12-volts to the small control terminal on the start-solenoid mounted near the isolator. This will close the start solenoid which will send power to the control terminal on the starter-mounted solenoid, which lets very high current to flow from start battery bank to starter motor. (12 volt source is available on isolator side terminal)

If this works, is does not indicate what the problem is, it just tells you all is well with your starter, Foretravel start solenoid, start battery bank and heavy battery cables. This is a simple and important test which tells you if the problem is in the low-current up front section or in the heavy current back section.

From my engine start wiring flow write-up you will find that there is a relay on the front panel that sends voltage to the isolator-panel start solenoid when Allison is in neutral and ignition key is in start position. A meter on the relay wires will indicate if Allison is sending its neutral voltage and if ignition key is sending its start position voltage.

Starting System Troubleshooting

© Barry Brideau 2003-2014