ALT Light Remains On for 40 Miles, then Flickers and Goes Out

[jmcnamer]

When I start my coach after it's been sitting for several weeks, my alternator light does not go out, and my tachometer does not register.  After driving it for 30-40 miles, the light starts to flicker, my tachometer starts registering, and the alt light goes out.  Initially the coach is charging at under 10V but then slowly the voltage creeps up after 30-40 miles then the voltmeter will register a normal charge, the alt light goes out, and the tachometer starts working.

When I check the alternator, it's fine.

Could use some help.

Thanks

Jody

[jfbolkovatz]

Jody,

What year and model of coach, please.

JoeB

[jmcnamer]

Sorry, that would be good information to have. 🙂  It's a 1997 Monaco Dynasty with the 300HP Cummins and Allison Transmission. 

Thanks for the reply

Jody

[OhReally]

Jody, sounds like you might have a failing voltage regulator or something else in the alternator that is changing with temperature. You say the alternator checks out fine but you probably aren't testing it under a load so while it looks ok it may not be. I don't know your coach specially but the tach is probably driven off an alternator electric signal so that's why it isn't working correctly either.

I would start by checking ALL connections between the alternator and the batteries, including the connections to the alternator itself. Simply looking at them is not a good check. You should remove, clean and replace every connection (large or small wire) you can get to. If that doesn't solve the problem, I would remove alternator and take it to a rebuild shop for check out. If you have an external voltage regulator you should probably also take that to the shop with you.

Good luck.

[jfbolkovatz]

Jody,

I had a similar problem and I believe your coach may have  similar wiring.  The ignition key only activate relays and 2 key ones are in the FRB below the driver, exterior. One is accessory and the other ignition. If the ignition relay is faulty the tach will not work. Mine was intermittent but once on everything worked.  Should try without the tach working tapping the relay firmly. it is all 12V so no hand jewelry.  Might work.

JoeB

[jmcnamer]

Thank you both for the reply.  I will try the relay and then move to the tracing if not successful.  I did replace the ignition relay last year, so perhaps there's an issue with the replaced part, or a connection.

Thanks again,

Jody

[bobdinsmore]

I had a similar problem of these two simultaneous troubles. Clean/tighten the connection on the alternator where the ALT signal comes from and also the grounds behind the dash lights/instruments. It fixed my problem

Bob Dinsmore 2000 Diplomat

 

[Guest bobstromain]

Just went through the same problem.  Had to have the alternator rebuilt.  My tach never stopped working though. 

My alternator  had 3 small wires  The rebuild shop converted to a single wire.  I was concerned about that, but during my test drive everything worked as it should.

Bob St Romain

04 Windsor

[jmcnamer]

I really appreciate the help.  I will be working on this problem this weekend.  I'll let you know how it goes.  I'll always welcome other ideas too. 

Thanks again.

Jody

[Rich Cutler]

Mine was entirely intermittent.  On and off end never knew when that would happen.  58000 miles on coach,  finally had to change idler bearing due to squeal and had them look at alt at same time.  Bad.  Replaced both.  Also, lost two of the bolts on the exhaust manifold. UGH expensive  visit.  Manifold was eaten by paths of exhaust gas.  Explains noise back there.  Now very quiet.  

Rich Cutler

06' Windsor