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bwilless · 07-25-2021, 04:24 AM

I’m having an issue with my 1998 Winnebago 36WL Diesel Pusher and need some help. The coach has a 5.9 Cummins.

There seems to be large voltage spikes on the truck electrical system. I first noticed this while driving and my radio would reset. After careful observation, I noticed that the voltage gauge on the dash would also spike higher when the radio reset. At first this is all that would happen. Eventually, I would notice crazy voltage swings; the voltage gauge would swing from <6 volts to >14 volts 30 times in less than 1 second. This spike would jack up other systems on the coach. I suspect this spike took out my Norcold control unit. More on the effects of the spike in a minute.

My first thought was that the voltage regulator was bad. On my coach voltage regulator is part of the ECU and instead of buying a new ECU, I wired up an external voltage regulator from an early Ford (https://www.amazon.com/dp/B000C9QI96...roduct_details). With the new voltage regulator, I had the same issue. So the alternator is making the voltage and if the voltage regulator is good, it must be the alternator not taking direction from the external voltage regulator.

I put a new alternator on the coach, and put the voltage regulator wiring back to the ECU. Started the coach and had the same issue. So I wired the external regulator back and still had the same issue.

I disconnected the house batteries and put a multi meter at the truck battery with the coach running and do not see any voltage spikes at the truck battery.

What else in the electrical system could be causing these wild voltage swings?

Just to make my job harder, the voltage swings also takes out a relay or other electrical component somewhere that feeds the truck control systems.

So it looks like this, get the truck started observe the wild voltage swings, dash warning lights come on, like the abs failure light. At this point I know that power to the system went bad. Turn off the engine and try to start the coach, all power is dead. No dash lights, I can’t even turn on the emergency flashers.

I’ve been able to get the system back live again a few times. Once I just disconnected/reconnected the truck batteries and that cleared the issue. Another time, it just started working again after ~1 hour. Another time (after waiting a few days), I found a +12v stud in the front electrical box that feeds the truck electrical system. I found the stud had no voltage, I jumped a wire from a 12v relay in the box to the stud and the flashers started working (observed sparks so something was loaded). Checked the dash and I could start the coach again. After the next test, I can’t get the power back on to even start the coach.

I’ve recently replaced the ignition switch at the dash, so I don’t think this is the issue. The emergency flashers should work without the ignition switch being on.

Thoughts on next steps. I’m really working two issues. . . .

First how do I locate the relay or electrical equipment that’s keeping me from starting the coach. I need to solve this to work the root cause issue. There’s a bank of ~10 30A relays in the front electrical box, I thought about rotating them one position to see if the power comes back on. I think I found a schematic for my coach, but I can’t follow it.

Second, how do I isolate the different truck electrical systems to locate the component that’s causing the voltage swings? I have run the truck with the voltage regular wired incorrectly, I don’t think this harmed anything, but did note that the alternator was not putting out any voltage, the dash voltage gauge showed ~12 volts, and I don’t recall seeing any voltage spikes.

Thanks for any insights, recommendations observations that the group can offer!

Skip426 · 07-25-2021, 10:07 AM

Within the first 3' of cable from the chassis battery positive post , there is a LARGE 12 volt circuit breaker , that protects the cable running to the dash power stud . Mine is on a plate , on the frame rail behind the battery tray , only visible from the ground looking up . Poor connection there could be an issue .

Power cable from the alternator , connects to the chassis battery power cable at the starter . connection there has to be checked too.

This schematic ( from 1996 ) should help .
Picture shows starter relay and 12 volt circuit breakers , one for dash power , second for engine heater grid ( your chassis may have 3 C/Bs in this area. )

Skip426 · 07-25-2021, 10:16 AM

Sorry , the schematic I posted is for Freightliner with Caterpillar 3126B .

Here's one for Cummins engine .

bwilless · 07-25-2021, 02:06 PM

Thanks Skip, I’ll get under there in a while and check it out.

bwilless · 07-25-2021, 05:23 PM

I found that the main power connections at the starter motor were bad. There was lots of corrosion and power to the 12v circuit breaker was flaky. I cleaned up the terminals and all is well! No more voltage spikes. Thanks for the help Skip, you got me to the source.

Brian