Erratic Voltage at Auxiliary Battery.

[rockdude]

I have a 1999 E350 with the auxiliary battery under the side door. All components to it from the engine battery are stock .

Situation- A few years ago my auxiliary battery would not hold a charge, I put my volt meter on it and was get like 8-9 volts coming off the leads. Today, I decided to work on it. Tested the leads at the auxiliary batter and was getting no voltage. Went and bought the only two components I could think that could be bad. The Rely (Starter like rely) under the battery on the fender and the Rely Fuse F20 in the BJB.

I Replaced them, Bingo I got 14 volts. Later I restarted the van and tested it again and have like 9 volts. Tuned the van on/off again and like 8 volts. I replace the old Fuse F20 back into the BJB and restart the van, bingo 14 volts, I turn it on/off again and back down to like 10 volts. so on and so.....

I am not very electrically incline but what could cause the variation in the voltage? What am I missing? The main battery always have 14 volts.

[rallypanam]

Did you put a new battery in? 12v components will often give confusing results if the battery is not good and fully charged. And if two years ago your battery was at 8-9 volts, it's hella dead now.

Also, check grounds, they will also give odd results.

[carringb]

Yup. Your cells are dead. If it sat discharged that long, its probably shorting though the battery, which is what's blowing that Maxi-fuse.

[rockdude]

Originally Posted by rallypanam

Did you put a new battery in? 12v components will often give confusing results if the battery is not good and fully charged. And if two years ago your battery was at 8-9 volts, it's hella dead now.

Also, check grounds, they will also give odd results.

No battery installed, I will get one this weekend and we will see it if helps with the 8v-14v seesaw.

[rockdude]

Originally Posted by carringb

Yup. Your cells are dead. If it sat discharged that long, its probably shorting though the battery, which is what's blowing that Maxi-fuse.

Ya, the Battery was fried so I pull it out. I was getting the volt reading off the battery terminal clamps without the battery attached.

[rockdude]

Moving forward but no solution. Gosh, I wish I knew more about electrical things.

So when I turn off the vehicle and pull the F20 relay out of the fuse box crank it up then turn it off and then replace the F20 fuse again I get 14 volts at the Aux battery terminals and in the fuse box. The next time I start the vehicle I will get some erratic low voltage at the aux terminals and Fuse box. So something about turning off/on the vehicle and and removing and replacing the fuse resets it and I get 14 volts. But the second time I start the vehicle it has low volts.

Its not the relay. I tested the Fuse box in the F20 holes and get the same type of reading as I get at the aux battery terminals.

The Aux Battery relay on the wheelwell test good all the time as does the Transit Plug.

So something between the fuse box and the Transit plug or Aux Battery relay could be bad?

Any ideas as to where to look next?

[arctictraveller]

Did you install a new battery?

[rockdude]

Originally Posted by arctictraveller

Did you install a new battery?

No, never made it to town. We had a wildfire today with a mandatory evacuation meaning if left the house I wasn't going to get back into the evacuation zone. So I just stayed homee and tested everything I could with the volt meter.

[arctictraveller]

You can get funny readings with out the battery in the circuit.

[rockdude]

Finally got the new battery in and its not showing any charging from the alternate, Showing 12.6v with the engine running or with it off.