Truck alternator keeps failing/blowing. Just replaced with a 90 amp unit stock. Something in charging system is failing as truck will only run on battery power then die. Where is the voltage regulator on this truck? I cannot find it anywhere on firewall or what does it look like? What else could be doing this? Not charging at battery terminals. Not getting the 13 or 14 volts at battery terminal when meausured with volt meter.

Where is voltage regulator and what does it look like? is it square box?

Thnks,

Wizard

What are you working on? Year, model would be helpful.

Year?

Could be either this on pre 69 cars with single prong alt fields:



Or this on post 70 on dual prongs alt fields:

89 Dodge truck W100 4x4 automatic. Truck was running good. Alternator failed. Had it tested at Autobone. Put a 90 amp on it, also at that time I bought a voltage regulator, like the one pictured in the below post. I could not find that voltage regulator anywhere on that truck or firewall. Sometimes voltage regulators go out and then it takes out the alternator also or is on the fringe and takes out alternators. I took voltage regulator back to Autobone because I could not find it. Possibly 89 trucks look different and they sold me wrong part.

Wizard

That is because in an 89 Ram it's got TBI and the regulator is part of the computer.

If that portion of the computer fails you can add a regulator like the bottom one in the above post.

In order to quit guessing and spending money on things you may not need get a meter and tell us what voltages you are seeing. That will tell you if the alternator is being full fielded.

Thnks. I did not get a chance to check voltage on the 2nd alternator fail as it failed last night. When I did put the new alternator on at first I was getting 12.53 or so at the battery terminal. Then when I turned on the lights it dropped to 12.35 both of these voltages were holding steady for 2 minutes with no drop. I drove the truck about 100 miles with no problems then the alternator stopped charging last night. Did not take a voltage measurement yet. Battery dead from only driving it for a 1/4 mile then returned home before truck died.

Autobone says they can order a computer.

Your alternators aren't charging at all. At least not getting to the battery or anything else in the truck.

Might be a computer problem, might be wiring.

CHARGE YOUR BATTERY!

Then check voltage at the big stud on the back of the alternator and it's case. Engine running I'd like to see 13.5 bolts or more, don't get too scared if you see 20 volts, it can happen if the charging wire is broken somewhere. Report back what you find so we can figure out wether it's a control problem or an out put problem.

You have three connections on the back of the alternator.

One big fat wire that is the output.

Two smaller wires, one of which should have a steady voltage on it at or very near the same voltage as the output wire.

The other smaller wire is what controls the alternator output and comes from the regulator. It will have a lesser voltage on it compared to the other two.

If it turns out to be a regulator issue

http://store.alternatorparts.com/hd-external-voltage-regulator-conversion-field-replacement-kit.aspx

To add an external regulator instead of replacing the computer.

No voltage at battery terminal right now. Alternator not charging. Dad took it to a repair shop this morning. Did not want him to do this but I am at work and he only trying to help fix. Told him to stop as shop will be costly. I am with you, believe computer is problem. I called Autobone and Autozone. both can get computers for around $160.00 I can go to junk yard and probably get one for $10.00 from guy I know and take the chance. Also Autozne said they would take back the fried alternator now at no charge and give me a replacement. Question I did ask autobone is that computer specific to that year? They don't know and they said they do not see a spread of years that computer will cover. They did say you can use a D or B model (truck or van) for the same year. If I go to junk yard and pull one out of a 87 truck will it work or are things different?

Rockauto shows 2 possible computers for an 89 W100 with automatic (I assumed you had a 318, if not then this does not apply)

One for California emissions, one for federal emissions.

It's a bit more complicated if you have the V6. One fed, two Cal, depending on date of manufacture of vehicle.

(1) cant beat that pricewise (2) generally no returns on electrical parts so you are doing something right on that situation. (3) it sounds like all of that year will work so I wouldn't be afraid to grab one from any 87 & even on the slim chance that it is a no go (on the model) for $10 you ain't hurt hardly at all. another option would be to get the flat reg in the pic & wire it in (it s easy). In the meantime I would absolutely drive something else & when you get it taken care of, slo charge the battery back up on a charger as opposed to using the alt to do it.

Slow down or waste a lot of money.

No voltage at which terminal? The fat one on the alternator? Do you have any voltage at the battery?

Shop that my dad took truck to found problem. They said looks like mice were knawing at wires going into computer. They repaired wires and said truck is working fine. Will check everything once I get to it to see what they did and double check everything in working order. $75.00 bill included delivery of truck to my dads house after shop drove my dad back about 3 miles to his house one way.

Was no voltage at positive battery terminal when truck was running.

That is not possible.

Unless you are calling something else the "positive battery terminal". The positive battery terminal is the lead stub sticking up out of the top of the battery that your starter cable hooks to.

Yes, that is where I took my measurement at. The positive battery lead stub.

You came out real good there.

Could have saved the $75.00 bill but it was 3 oclock in the morning and I didn't feel like troubleshooting as had to be at work at 7 AM. Would have seen the damaged wire after learning about where computer is and built in voltage regualator and would have repaired myself.

Thnks for all the help everyone. Truck is running good now. Drug a 70 challenger up to Fall Carlisle last night at 1 AM and got home at 4 AM after setting car up for sale there.

Wizard

On truck with regulator built into the computer, just add 70's style electronic regulator - requires you to rewire the field to the new regulator, and an ignition "ON" on source to the regulator. Way easier and cheaper than getting another computer . . .