Electrical Issues

[emb2060]

Alright guys, I've been reading on this forum for awhile but hadn't joined until now. I'm having electrical issues that I can't seem to trace and I figured this would be a good place to come for advice. I have a 1986 c30 with a factory PTO-driven dump bed (flatbed). About 2 weeks ago I went out to start the truck to haul some items for my dad and the battery was dead. I quickly realized the alternator wasn't charging. I took the alternator to get tested at O'Reilly and it tested good four times in a row. I have since gotten a new alternator just to eliminate that possibility, but the problem is still there. I'm getting power to both hot wires on the alternator. I've checked all the grounds on the truck that I'm aware of, pulled them off and cleaned them. I replaced all my fusible links with inline 15 amp fuses. The problem that I've noticed is in the brown exciter wire that tells it to charge. If the plug is unplugged from the alternator, the brown wire gets 12 volts with the key on as it should. However, when I plug it into the alternator, it's dropping to about 9.5 volts or so. My fuses are all testing good. I even tried splicing into another key-on 12v wire and it still dropped to about 11.5, not enough to make the alternator charge. I'm kind of lost for where to go from here and was hoping some of you fine men and women would have some ideas or advice for me. I'd truly appreciate it.

 

[Matt69olds]

You need a much larger fuse than 15 amps to replace a fusible link. I wouldn’t be surprised if you find the fuse blown. Take the fuse out, install the correct gauge fusible link. If you absolutely insist on a fuse, you’re probably going to have to use a MaxiFuse and the proper holder for a 40 amp fuse.

What’s the voltage at the charge wire stud on the back of the alternator? And what’s the voltage at the fuse box with the engine running? If there is a big difference, you have a bad connection somewhere.

 

[emb2060]

I already checked the fuses I put in, they’re not blown. I got 15 amp fuses because the guy at O’reilly said he redid his old truck with inline fuses and the fusible links were 14 amp. Maybe he was wrong, but they aren’t blowing.

The voltage at the back of the stud is over 12v. Where should I be measuring at the fuse box?

 

[WP29P4A]

Sounds like the cashier at O'reilly's is mixing up amps and wire gauge. Never take advise from cashiers, or people with less than 7 fingers.

@Matt69olds advise is absolutely correct. Also the fusible links you removed were "slow blow" type fuse, what you replaced them with are fast blow fuses. A couple of internet searches to help you understand what you are working with, before you start re-engineering your electrical system will save you time in the long run.

FYI, not trying to sound high and mighty, LOL. I have made the same mistakes myself. There are several types of fuses.

 

[emb2060]

Sounds like the cashier at O'reilly's is mixing up amps and wire gauge. Never take advise from cashiers, or people with less than 7 fingers.

That sounds more likely. I will order the right links.

 

[Snoots]

For simplicity they call it '12 volts'. Your alternator should put out 13.6 vdc. Your alternator actually generates AC (alternating current). There are 6 diodes in the regulator. 2 for each phase (there are 3) of the alternator. Each diode will drop/lose about .7vdc. 6 x .7 = 4.2 vdc. Subtract that from 13.6 and you have 9.4 vdc.
Sounds like your alternator is okay.
Check your bulb at your voltmeter (in the truck). If it's blown, your alternator will not turn on. Just turn the ignition key to the on position and see if you have a light. Go from here.

BTW, PIX dammit! We need pix of your truck!

 

[emb2060]

For simplicity they call it '12 volts'. Your alternator should put out 13.6 vdc. Your alternator actually generates AC (alternating current). There are 6 diodes in the regulator. 2 for each phase (there are 3) of the alternator. Each diode will drop/lose about .7vdc. 6 x .7 = 4.2 vdc. Subtract that from 13.6 and you have 9.4 vdc.
Sounds like your alternator is okay.
Check your bulb at your voltmeter (in the truck). If it's blown, your alternator will not turn on. Just turn the ignition key to the on position and see if you have a light. Go from here.

BTW, PIX dammit! We need pix of your truck!

Pics As requested.
I’ve had the alternator tested and even bought a new one to be safe and it isn’t working. What I’m saying is that the brown exciter wire is supposed to be 12v to make the alternator charge, correct? It’s getting that voltage until I plug that connector into the alternator, then its voltage is dropping enough that it doesn’t excite the alternator and tell it to start charging

 

[emb2060]

Pics As requested.
I’ve had the alternator tested and even bought a new one to be safe and it isn’t working. What I’m saying is that the brown exciter wire is supposed to be 12v to make the alternator charge, correct? It’s getting that voltage until I plug that connector into the alternator, then its voltage is dropping enough that it doesn’t excite the alternator and tell it to start charging

Sorry, didn’t mean to add the pic of the motorcycle

 

[Matt69olds]

I’m not exactly sure how the brown exciter wire works on a truck with a volt gauge and no idiot light. The way an alternator exciter circuit works with a light is ignition power goes to the idiot light, out the light on the brown wire to the alternator. That’s what the regulator sees to know the ignition is on. Once the alternator is spinning, the regulator is suppose to apply power to the brown wire. Since you have power on both sides of the light, it stays off.

The regulator supplies a ground when the alternator is t charging. That’s why the light comes on with the ignition on, engine off.

I have never check voltage on the brown wire with the engine running, so I have no clue what it will show.

Did you verify voltage at the alternator stud? With the engine running, it should be around 14 volts.

 

[mshawn]

Sounds like the cashier at O'reilly's is mixing up amps and wire gauge. Never take advise from cashiers, or people with less than 7 fingers.

Lol ,good rule of thumb!!!!!

 

[emb2060]

I’m not exactly sure how the brown exciter wire works on a truck with a volt gauge and no idiot light. The way an alternator exciter circuit works with a light is ignition power goes to the idiot light, out the light on the brown wire to the alternator. That’s what the regulator sees to know the ignition is on. Once the alternator is spinning, the regulator is suppose to apply power to the brown wire. Since you have power on both sides of the light, it stays off.

The regulator supplies a ground when the alternator is t charging. That’s why the light comes on with the ignition on, engine off.

I have never check voltage on the brown wire with the engine running, so I have no clue what it will show.

Did you verify voltage at the alternator stud? With the engine running, it should be around 14 volts.

It isn’t, I’m barely getting voltage at the stud when the truck is running. I’m getting 12 volts when it’s not running on both the stud and the red wire in the plug. I’m getting 12 volts on the brown wire in the plug with the key on when it’s not running, but drops to 9 or so as soon as I plug it in. So my assumption is that it’s not seeing the voltage it needs to charge, but I can’t figure out why.

 

[Jgonick]

With gauges- I believe the brown wire - BRN-25 becomes (at bulkhead) BRN/WHT-130 that should splice with ORN-300 that connects to ignition switch- (or just connect at ignition w/ ORN-300)

 

[Jgonick]

Does your truck have gauges or idiot light?
What type of alternator? SI or CS? - Probably a CS series- is the wire terminal PLFS or PLIS ?

also BRN -25 (brown wire)-supplying field current excites "starts" the alternator. It doesn't tell the alternator to charge or not.

Double check:
#1. The B or Batt terminal should be connected to the electrical system's main distribution point or less optimal- to the starter motor that connects to battery + terminal or even less optimal directly to + terminal of battery.

#2 BRN-25 should be connected to L terminal (assuming CS w/ PLFS) should go through idiot light or have roughly ?? 50ish Ohm ?? resistance on wire ( thus the BRN/WHT 130 wire on trucks w/ gauges-see above post)

#3 Ensure good ground connection between bare alt case & mounting brackets-

TECHNICALLY that is all you need to hook up- However:
#4 for better performance hook S terminal "remote voltage sensing terminal" to electrical system's main power dist point(bus bar, fuse panel, etc..) [_I believe mine is hooked to the starter motor that connect to + terminal of battery] If not connected, the alternator will/should revert to internal sensing output settings.

I would definitely replace your fuse-able links.

 

[Big Ray]

do you need an oversize permit for those pipes?

 

[emb2060]

do you need an oversize permit for those pipes?

Haha no idea, not my bike. Just something I saved to show my father in law. I have several, but that’s not something I’d do