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Old 10-06-2019, 01:06 AM   #1
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Brand: Thor Motor Coach
Model: Palazzo 33.2
State: Georgia
Posts: 211
THOR #8078
Trombetta relay replacement

The engine generator no longer charges the house batteries and shore power will not charge the chassis battery. I ran diagnostics. After the engine has been on for 60 seconds the BIRD sends a 12v signal to the Trombetta relay and it clicks, but there is no voltage change across the chassis/house connections at the relay. I verified this by finding no voltage change at the house battery. My questions: 1. Am I correct that the Trombetta relay is defective? 2. Should I replace with the same part#? 3. There is a large disconnect switch for the chassis battery. Is it safe to disconnect the chassis battery using this switch so I can safely replace the relay? Will I lose any settings in the engine control unit when I cut power? 4. Anyone tried this replacement successfully? Thanks.
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Old 10-06-2019, 02:42 AM   #2
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Brand: Thor Motor Coach
Model: 2013 ACE 30.1
State: Alberta
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THOR #2631
Attaching a schematic I scrounged off the Forum from another contributor who was having battery problems.......does this seem to represent your coach as well? If so, I think the relay marked ISO represents the Trombetta.


1. If the Trombetta relay (also called interconnect or isolation relay by some) has been operated by the BIRD as you say, you should see the same charging voltage level from the alternator on both main terminals on the Trombetta. You could also connect your voltmeter probe to ground and measure the voltage (+ probe) on each main contact of the Trombetta (two readings) and if the two values measured have less than 0.2 volts difference, the relay is considered closed and functioning. Greater then 0.2 volts difference and the contacts are considered bad. Replace the relay. This would work the other way too (shore power connected; converter (or inverter/charger) charging coach batteries and Trombetta then closes to connect charging voltage to chassis batteries.
2. I usually suggest changing failed parts with the same part # replacements mainly to ensure that re-installation is a no brainer......same dimensions; same connection points; same engineering spec to match OEM design. If a part continues to fail regularly and has clearly been under designed then using an equivalent with superior specs can be an alternative to OEM. You have to do some homework to make sure the replacement will fit all the requirements.
3. Yes using the chassis battery disconnect and coach battery disconnect (if equipped) will work plus no gen running; no shore power connected for added insurance. If you are replacing the Trombetta, which should have connections to both battery strings......you should isolate both battery strings for safety. The other option is remove the main ground connection to chassis for each battery string (coach and chassis) to ensure the batteries are not connected. You will likely have radio memory loss and possibly Firefly settings if equipped; AGStart settings possibly; not sure if the PCM will also have to re-learn its settings by driving the coach for x miles. I am sure others can add more specifics here since I am not familiar with your coach details.
4. I am sure they will chime in......
Attached Files
File Type: pdf Palazzo Battery Compartment Wiring.pdf (183.6 KB, 62 views)
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Old 10-06-2019, 07:28 PM   #3
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Brand: Thor Motor Coach
Model: Palazzo 33.2
State: Georgia
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THOR #8078
Thank you Javelin. I did check the voltage after the BIRD fired off its 12v signal to the Trombetta relay. WIth the engine running the chassis side is 14.1 and the house side was 12.5, so the relay must be broken. It seems safe for me to replace it if I am careful to cut power. I like to assess risk if I botch the repair but this one seems OK to proceed.
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Old 10-06-2019, 07:59 PM   #4
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THOR #2631
I think you just found your problem......good work! Since the two battery strings terminate onto the Trombetta (isolation/interconnect relay) just make sure to disconnect the two battery strings (common chassis ground cable off the battery post on each string works if you don't have individual disconnects) to prevent any welding/sparks if either relay cable end touches chassis or some other unintentional connections. You can also use your voltmeter to ensure both Trombetta cable ends are dead before starting to disconnect them for the repair. Many folks also slap a wrench onto the battery nuts and start swinging it without realizing that wrench can become a dangerous conductor if it hits the other battery post etc.



It is also a good habit when sticking arms and hands into battery boxes to remove metal watches and rings......it is amazing how fast those items will vaporize along with potential burns to you from the heat generated. The battery voltage is not dangerous, but the current can be. You will be fine just take your time and work safely. End of Motherly advice.....I have seen it happen is all.
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Old 10-06-2019, 08:52 PM   #5
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Brand: Thor Motor Coach
State: Florida
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THOR #14426
I had the same problem and replaced both the trombetta and the BIRD, only then did I find it was a fuse all along. Look for a 7 amp fuse on the positive line going to the ignition. It is a medium 2 blade type fuse. Mine was in a small black inline fuse box with a 7amp sticker on the side.
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Old 10-06-2019, 10:00 PM   #6
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Brand: Thor Motor Coach
Model: Thor Tuscany 40DX
State: Colorado
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THOR #5043
My Trombetta failed just as your has. The relay just cooks itself to death from too much power dissipated in the coil, about 30+ watts. Bet you can't even leave your hand on it after a few minutes. I found a White Rodgers 15V coil unit with silver plated contacts at about the same price. The 15 volt coil is important. Much better solution.
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Old 10-06-2019, 10:26 PM   #7
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Brand: Thor Motor Coach
Model: Palazzo 33.2
State: Georgia
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THOR #8078
Thank you. I did check all the fuses which were fine. I verified BIRD working correctly because it sends a 12v signal which is received by the Trombetta at its+ switching terminal. Then the Trombetta solenoid clicks but does not close the high current battery circuit.
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Old 10-07-2019, 12:06 PM   #8
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Model: Axis 24.1
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THOR #4366
Ours has pitted contacts so it works on and off. Picked up a continuous duty NAPA replacement for when I need to install. 100 amp contact rating. mounting will be a little different.
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Old 10-13-2019, 12:35 AM   #9
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Brand: Thor Motor Coach
Model: Palazzo 33.2
State: Georgia
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THOR #8078
Update: I ordered a new Trombetta solenoid, same part # as the original. After disconnecting the house and chassis batteries I replaced the old relay with the new one. Sure enough, after the engine runs 3 minutes the BIRD fires a signal to the relay, the solenoid clicks and you can hear the engine pick up the alternator load. There is now no voltage drop- it measures 14.0 on both posts and the engine alternator now charges both the chassis and house batteries. Success. The hard part was getting the old relay mount unscrewed.
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Old 10-13-2019, 01:19 AM   #10
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Brand: Thor Motor Coach
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THOR #2631
Congrats on your repair and also for providing the update. Now you are an expert on all things BIRD. No unexpected welding is a good sign.
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