First which car is master in group. you should have a 58 relay which if I remember correctly controls which car is feeding group relays. When you shutdown one of the car's mainline the other car's excitor feeds the common relays.When you pull the fuse your opening the power to keep the mg on from the other cars excitor. Sounds like an REL control... The 58's should be at bottom of center controller and are mech. interlocked. The a.c. sounds strange? Would have to look at a print, can't visualize it!

Do you have 90 and/or 91 relays?

There are some relays under the selectors,I'm not sure what they were.
And,I don't know if I have a 90 or 91 relay.

But monday,my buddy will show me and I will let you know.

Thank you!

They are power transfer relays from car to car when killing the power on one. Look at the tag on the controller and see if it's a REL.

I had a Westinghoue with AC on the DC side one time after replacing the rectifier I still the same problem. Then it dawned on me and I disconected the 110VAC lighting circute and my problem went away!!!! Ended up being the photo eye switch in the car panel. Sounds so easy now....

It ended up being low brushes on the exciter.
I know I had just replaced those.

9 relay was out. On those old REL's, if you get low exciter brushes you need to pull the 40 amp fuses and make sure your polarity is correct BEFORE you apply the DC back to the controller after you change the brushes and you crank the gen...... or you will do some damage.

Funny story to add to this.

My buddy decided he would clean the motor brush rigging and all with contact cleaner.

Well,he didn't let the cleaner dry long enough,turned on the unit and ran it.
A few sparks turned into a nice little fire.
All that oil and carbon dust burns good!

Shut the unit down,frantically searching for a fire extinguisher,which happen to be down at the bottom of a ship ladder.
Finally got it put out.

Got to love adjusters sometimes.;)

So True..You can get them back in polarity with a dry cell battery on the exckiter fields when it 1st cranks up, or for that truly adventurous type, you can take 2 orange sticks lift off 2 adjacent brushes from the exciter commutator while the exciter is turning and let them pop down on the exciter simultaneously. Arcs a litte, but more times successful than not.

As for cleaner...

Back in the day the companies used this god awful motor cleaner with the generic name of SS25. It would clean the hell out of a motor, but is a known carcinogen. Of course we knew nothing of that and just used it. I'm talking 1 gallon pump sprayers of the stuff and wash down Generators and Motors.

Evidently it's still being made..

http://www.chemsearch.in.th/th/Product%20Lable/ss-25%20label.pdf

Anyway we had a generator that would keep grounding out, and the company instead of pulling the genreator just sent the mechanic up with a gallon pump sprayer of SS25 and had him wash it out. This went on for about a year, until the mechanic.."ACCIDENTLY" filled up the pump sprayer with Varsol instead of SS25. Made a nice bon fire.. 😁

Anyway we had a generator that would keep grounding out, and the company instead of pulling the genreator just sent the mechanic up with a gallon pump sprayer of SS25 and had him wash it out. This went on for about a year, until the mechanic.."ACCIDENTLY" filled up the pump sprayer with Varsol instead of SS25. Made a nice bon fire..

Sometimes you gotta do what ya gotta do.........

90/91 power relays, just don't see these anymore....58 is in dispatching? You can actually reverse the excitor armature and the regulator armature and the car will sort of run......this happened to me on a job we took over from another company. After a day, we set all the taps back to original locations and swapped armatures...car ran like a champ!