Auto Generator Start Fix for 2007-2009 Contessa & Monterey


 Common Problems / Posted 10 months ago / 167 views

2007-2010 Beaver Contessa / Monterey Automatic Generator Start Problem and Solution

Problem: 2007-2009 Beaver Contessas and Montereys are wired so the Automatic Generator Start system (AGS) monitors the voltage of the chassis batteries and uses the house batteries for starting power. See figure 1. This is just opposite of the correct wiring. The AGS should be monitoring house battery voltage and automatically starting the generator to re-charge them when their voltage drops to a pre-set level (or if so equipped, the interior temperature reaches a preset level). The author checked a 2007 Patriot wiring diagram and verified that it was wired correctly and assumes this carries over to the Marquis.

Figure 1; Monaco’s Schematic for High Current, Low Voltage in Contessa & Monterey.

38081154 12v High Current

Solution:  This article will describe the step-by step procedure to correct this problem, using the author’s 2007 Contessa as the example. The solution is comprised of 2 separate operations; 1, Changing the battery sense feeding the AGS unit from the Chassis to the House batteries and 2, Changing the Generator Start voltage source from the House to the Chassis batteries.

Changing the AGS Battery Sense:

The red wire coming from terminal 3 on the AGS unit is the Battery Voltage sense wire. It needs to be disconnected from its current location and moved to a House Battery connection. On the 07 Contessa, the wire runs from AGS terminal 3 to VCM pin 7. (See Figure 2)

Figure 2: Original AGM Battery Sense



Verify your coach is wired the same. If not sure, remove the cable ties (you will need to do this anyway) and trace the wire from the AGS. Cut the wire about 1-2” from the connector. Tape or otherwise insulate the resulting wire tail coming from the connector. Crimp an eyelet terminal on the end coming from the AGS, label the wire and attach it to the House Battery stud on the PCB. See Figures 3 and 4. Reapply cable ties as needed. You have completed Operation 1.

Figure 3: Electrical Bay PCB

Figure 4: AGS House Battery Sense Hookup

Changing the Generator Start Voltage Source:

Extend the Generator to make access to the rear of it easier. Once this is done, remove all power sources. Turn off the inverter and battery charger. Switch house and chassis battery disconnect switches to OFF. Disconnect the + battery cables at the batteries. (If you don’t, battery voltage is still present in the rear electrical bay at the disconnect switches). Disconnect from shore power if possible. You will be working with metal tools and heavy gauge cable in the electrical bay and want to be sure there is nothing to accidentally short to.

Figure 5: Rear Electrical Bay

Referring to Figure 1; the Generator power is a 1/0 gauge cable connected to a 125A fuse. The Coach Power cable is a 2 gauge and is also connected via another 125 fuse.  Locate and remove one of the fuses (see Figure 6; Generator Power Location for location of cable in author’s 07 Contessa). Attach a tone generator to the insulated threaded stud that the cable is attached to (see Figure 7) and verify it is the correct by checking for a tone at the 12v start cable on the rear of the generator. (See Figure 8). If you don’t have a tone generator, temporarily ground the insulated cable stud/generator power cable and verify it is grounded at the generator. Remove the temporary ground.

Figure 6: Generator Power Cable.

Figure 7 Generator Cable on Insulated Stud

Figure 8: Rear of Generator

The next step is to construct a jumper cable to tie the generator start cable to the chassis battery supply. See Figure 9. The author constructed the cable from 2/0 cable, but 1/0 would also suffice. The total length of the jumper cable is 13” measured from the end of one copper lug to the end of the other copper lug (fuse not included). In addition to crimping the cable in the lugs using the crimper shown in the upper section of Figure 7, the author coated the jumper cable’s exposed copper with flux before inserting it into the lug, then crimped it and finally applied solder using a torch to ensure a solid connection. Use shrink tubing to finish connections. Then attach the 125A fuse to one end of the jumper cable. The author used a 5/16’ x 24, ½” long bolt and washer and nut with a nylon insert locking nut. Be sure it is tight. All parts needed for the jumper cable, including the crimper are available at NAPA stores. The author inserted the jumper in plastic cable sheathing for added protection prior to installation.

Figure 9: Jumper Cable w/Fuse

The author’s coach had an empty stud on the battery power side of the electrical bay and used it for the new generator power connection. See Figure 10. This stud was simple a bolt through the copper plate, so you will need to use a wrench (9/16”) to hold the bolt head while removing and subsequently tightening the nylon insert nut. Also, be sure to check the tightness of the other nuts on this plate. The author found one where the nylon had melted (suspect this was due to slight looseness). Replace any that show evidence of high temperature.

Figure 10: Open Chassis Battery Stud

To install the jumper, the author first placed a 9/16” wrench on the bolt head of the spare chassis battery stud. He then loosely attached the non-fuse end of the jumper to the generator cable insulated stud. See Figure 11. Run the cable above any existing cables behind the Big Boy solenoid. Next attach the fuse to the spare chassis battery stud, apply a washer and nylon insert locking nut and tighten. See Figure 12. Remove the wrench from the rear of the copper plate. Tighten the nut on the generator cable stud. Since the fuse is not held between 2 studs, it may bend slightly. This should not be a problem if all connections are tight and there is ample space between connections.

Figure 11: Jumper cable attached to Existing Generator Cable

Figure 12: Fuse and Jumper Cable attached to Chassis Battery side

Remove all tools and verify all connections. Reapply power. Turn on shore power. Hook up the + cables on the house and chassis batteries. Turn on the House and Chassis battery disconnect switches. Start the battery charger and inverter if necessary. Verify the generator starts. Retract the generator slide. Check/adjust the AGS settings for battery voltage and interior temperature.

Figure 13: Schematic, High Current, Low Voltage with AGS Modification

12V High Current w AGS Mod

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