Electrical Surge

[Renedy]

Having an issue getting my '75 W200 up and running.

Seems one of my issues right now is when the truck is running the volt meter will be resting nicely at 13.5 - 14 volts.

Then on a about a two second interval it seems like the volt meter will surge to 18 volts and drop to 8 volts.

The interesting thing is when I shut the engine off then turn the key back on without restarting the engine the volt meter will continue the same surge and recession as happened when the engine was running,

The volt meter is grounded to the battery directly and attached to the ignition accessory fuse.

Is it possible that the voltage regulator is faulty?

[DODGEBOYS]

its either the voltage reg or a curcuit breaker

[BrightRanch]

Agreed, I would get the regulator changed ASAP if its bad it will cook your battery.

[Renedy]

Still looking

Replaced the Voltage regulator, the electronic ignition control, and took the alternator in to local parts store to had them run it in their analysis jig and they gave it a pass.

I bought a new old stock wiring harness for the truck and it all seems to look good, cannot find any shorts or shaky looking connections.

I am thinking it still may be the alternator as it's the only old part left to the system.

Hoping that the test jig at the parts store is not able to test for fluctuation and I am getting bad info from their test.

Cant really think what else it would be.

[n1265]

I may be a little off base here, But if this happens with the motor OFF then I can't see where it is the ALT, or Voltage regulator.

Someone correct me if I am wrong, But I would suspect a short / dead cell in the battery, or ever a bad Volt gage...

[Renedy]

Test Stand

I thought the same things after the Voltage regulator, battery then gage.

I swapped battery first, no luck.

Then I eliminated the volt meter from the circuit, but I could still see the surging when I turned the dome and dash lights on.

I took the alternator to NAPA for a second opinion, and they too said it was OK.

My feeling is the alternator test stands at the car parts stores may be setup only to test if the alternator is generating 13 volts, which mine is.

But because the voltage regulator isn’t internal to the alternator maybe the test jig is not testing the alternator properly (or at least for what I am looking for).

None of my buddies has alternator I can swap test in and I don’t wanna spend any $$ on an alternator if mine is OK, but I am running out of other ideas.

[pwdave]

Renedy, change the altanator anyway, what you are describing is a diode getting ready to go. when it does the v.r. will hold it for a while then it will fry and the amp guage will peg out and cook the battery. (raised my hood once and my battery was round, closed the hood VERY easy and left for an hour.) these trucks are bad about doing this for some reason. bought a 78 new, did it several times in the next 10 years. Dave.

[n1265]

If you are still running into trouble,The only other thing I can suggest is to make sure your voltage regulator is grounded properly, It is grounded threw the case when bolted to the firewall. test the ground with a light if you have to...