91 Dodge Ram B250 5.9L Code 41 Charging Issue
 

Greetings, I have a 91 Dodge Ram B250 5.9L Van with a check engine code 41 (Generator field not switching properly).
The battery and alternator were checked and both are working fine. Actually, we put in a new alternator and the problem still exists, so replaced the old one which is just over a year old.
The battery is not being charged.
The large wire on the back of the alternator is not hot.
I have been advised by a mechanic who specializes in electronics that I need a new ECU (computer). Does the computer regulate the voltage? There appears to be a voltage regulator on the alternator. We will be installing this tomorrow, but I'm looking ahead in case this doesn't solve the problem.
Thanks for your advice,
Dan

It should have +12 volts on it as long as the battery is connected. Sounds like you problem is a break in the large red wire between the battery and the alternator. Some models have a large inline connector...check that for corrosion.

Problem Solved
 

UPDATE:
I replaced the original battery isolator with a new 90 amp isolator and it did NOT solve my problem, but nice to have a new one. I finally changed the Engine Control Computer (ECC), and the problem is resolved. Apparently, the voltage regulator is controlled by the computer in my 91 Dodge. Engine code #41 no longer exists. Replacing the computer was a 15 minute job.

The new computer was available, next day, at my local Advance Auto for $175, with a one year warrantee.

I have not checked into the engine code #37, but will address that when it resurfaces as an engine code. Codes were erased while solving the first issue. Maybe the new computer has resolved this code also.

As a side note, I was having a slight problem with a backfire within the first 5 minutes of driving the RT. I assumed it needed to be warmed up. I did a full tune-up and the problem still existed. While solving the first problem (#41 above), I learned that the timing on this year/model is controlled by the computer. Since the new computer, NO backfire!!!!! Hoping this problem is solved also. Hoping to get better gas mileage also.

Thank you all for your help!
Happy Thanksgiving,
Dan Hallinan
91D190P