Prevost Ignition Trouble

[jok]

I have been having some problems with my 1990 Prevost ignition. Frequently I turn the key to start it and the idiot lights come on for less than a second, or not at all. When that happens it will not turn the engine over and nothing that should be on when the key is on will come on (radio, fan, etc). I try again (sometimes 2,3 or 4 times) and it will work as it should for awhile. I had replaced the Ignition Switch a few years ago and it tests okay with a meter. When the ignition switch fails to activate anything there is no power to the circuit breaker for the Ignition (CB5) or the buss bar in the electrical panel below the drivers window. When the ignition is working correctly there is power to the circuit breaker and buss bar.

I think I may have found the problem, but would like some input before spending money on parts. When the ignition Malfunctions the Ignition Coil (pictured) has power to the large right lug and small left lug. When the ignition works Correctly there is power the the large left lug, large right lug and the small lug on the left. When it is malfunctioning I leave the key in the run position and hit the coil with a plastic mallet and everything works, for awhile.

I think a new coil will take care of the problem. But maybe someone has had similar problems and there could be more to it. Am I missing something.

Thanks,
John

[Len Silva]

I think that the HDA (Hammer diagnosis Aid), assuming all the connections are clean and tight,  pretty much proves it's the solenoid.

Len

[TomCat]

My Thomas uses a similar 'master power' set up in it's electrical box next to the drivers seat.

When I installed the charging ciruit for my Onan genny, I used a 12 volt solenoid to connect the coach electrical system to the genny battery for charging...works perfectly.

The four connections on my 12v solenoid were...

large post A: 12 volt load (out)
large post B: 12 volt supply (in)
small post A: 12 volt solenoid energizer
small post B: solenoid gound

...and I feel yours are likely the same, but a VOM should help you assure you're making the proper connections.

HTH
Jay
87 SaftLiner

[rip]

I have an 85 Prevost and had the same problem.I went to NAPA and they had one in stock. A few months down the road I had the same problem.I bought my next coil from Prevost and had not a problem since.That was over 4 years ago and the part was cheaper.I buy almost all my parts from Prevost and found the quality and price to be to be very good.
     Don

[luvrbus]

Jok, those are a constant volt solenoid nothing special only the amp rating what kills that system it is low voltage and bad grounds and you tapping with a hammer and it works sounds like a ground problem.
I have always found when the are bad they are bad no in between.    

good luck

[jok]

Len, I was not familiar with phrase "HDA (Hammer diagnosis Aid)", I like it!

I checked the ground, which appeared to be okay, and then ran a new ground. Still had the same problem.

rip, you are right about Prevost parts. On Tuesday I called Prevost and got price of $19.86 delivered. The new coil arrived today. A new coil at Granger was $38.75.

I installed the new coil/solenoid today and during a few dozen tests it performed flawlessly. With the old coil/solenoid it would fail about 10% of the time, and about 50% of the time after it sat for awhile.

Thanks for the help,
John