whosdunit

My 91.5 ,d250,,,chareges good and has always kept the battery up BUT!! When sit'n at idle the amp needle bounces between 14-18 ,and the dash lites pulsate . Has a new voltage reg., turn sig., brake's ( heater blower),,causes the amp needle to bump back& forth sooooooo now what to look for????

bannerd

Check the alternator? Autozone does it for free, should be running at 14.8V

KRB

I chased that gremlin for years. Mine pulsed several times a seond. I added grounds and checked all the likely suspects. Turned out to be a bad spot in the wire. The only way I found it was the loom laying on the left front fender started showing a green fuzzy dot on it. I dug into and found the wire almost corroded in two. Soldered it together and now have solid lights.
Good luck!

whosdunit

O' man,,,i'd rather have to buy a new alternator , to chase more bad wires. I will have alter., cked ,,thanks KRB ,that's where i'll start my search.


whosdunit

KRB

Amen brother. I tried EVERYTHING (except dissecting the wiring harness) and finally just gave up and figured it would eventually show itself one way or another - which it did.

Hope yours is simpler and easier. How fast do they pulsate?

gyman98

Try running a ground to your new VR

whosdunit

I wonder what it woul cost to completely strip the truck and have it ,,,COPPER PLATED??????

j_martin

The wiring harness in these things, except for a few undersize problems, is actually pretty good, with weatherpack connectors, etc.

What usually kills them is when a tech pierces the insulation for testing, and doesn't repair the wound with a little dab of liquid electrical tape. Salt and water get in and do their thing under the insulation and cause faults that are hard to find.

gorms

I had a problem pulsing at idle that was getting worse. Tried new reg, already had seperate ground and new wires to the reg and I finally checked the water in the batteries, topped them off with fresh acid and it's smooth as silk now.

whosdunit

True,True ,,True.I'v learned to use a med., size safety pin taped to my tester.( makes for smaller holes).


whosdunit.

Rampage1967

Mine did that for several years . . .new diodes & tunring the commutator rings in my alternator solved it. i had a bunch of bad diodes.

Jim Lane

Bad diodes in the alternator will cause cyclic fluctuations of the output as the engine speed increases and will show themselves as the load demand increases.

Either one pos or neg diode in the output trio will cause the smooth 3 phase output to miss 1/3 of its output and cause the lights to pulse, the battery will buffer the pulses to sometimes a flicker, the rated 120 amp output will also be considerably less.

It is fairly simple to check them after the alternator has been disassembled.

If you want to see a hyperactive ammeter, check out the mopar charging system of the old 1968 Dodge Charger or 1970 Road Runner, they would swing from center to pegged off idle and follow the lope of the 320* camshaft.

Jim

KRB

I wish mine had been as easy as R&R the alternator! Hope that's your problem.

whosdunit

I don't know if I did right or wrong,,,, but I took grd., cable off of the battery w/ trk., run'n,, amp needle was steady as it should be,,put cable back on,,,,went back to pulsating,jump'n bounce'n did this help me isolate my problem.

whosdunit

j_martin