1977 K10 generator light quit working not exciting alternator

[blackbird454]

Hello everyone I have a 1977 k10 350 non a/c truck if that matters. Recently discovered after a heater issue that the generator light is no longer lighting up which in turn isn't exciting the alternator to create power. I however used a jumper wire to the #1 terminal of the alternator and it started charging. Can I create a dummy light to circumvent the original or has anyone else had this problem. Also Alternator charged at perfect voltage after hitting it with 12v to excite it. Thanks so much. Edit- Can I just run a switched wire possibly to a toggle switch to excite the alternator once then switch off or does the exciter wire have to run with a inline resistor to avoid backfeeding?

 

[Ricko1966]

Hello everyone I have a 1977 k10 350 non a/c truck if that matters. Recently discovered after a heater issue that the generator light is no longer lighting up which in turn isn't exciting the alternator to create power. I however used a jumper wire to the #1 terminal of the alternator and it started charging. Can I create a dummy light to circumvent the original or has anyone else had this problem. Also Alternator charged at perfect voltage after hitting it with 12v to excite it. Thanks so much. Edit- Can I just run a switched wire possibly to a toggle switch to excite the alternator once then switch off or does the exciter wire have to run with a inline resistor to avoid backfeeding?

You can run a socket and light bulb 1 end of the socket to any keyed 12v source other end of socket to alternator terminal 1 it will work just like the dash light but it will be where ever you put it. Have you checked your dash bulb?. If you are super lazy you can hook a buzzer or moped horn to terminal 1 and to keyed source under the hood. You turn the key,you hear the buzzer,you know your circuit is good the truck starts the buzzer quits you know you are charging

 

[Jgonick]

Recently discovered after a heater issue that the generator light is no longer lighting up

It's power comes through (sort of) the heater fan switch (at least the wire running to the switch). On a 77 there will be a brown wire (brn-50) feeding the heater switch but an orange wire (orn-939) comes out of a connector on the way into the switch. That orange wire feeds the exciter. Depending the heater issue- check the heater fuse. (same fuse the exciter uses). Then check the connection I mentioned above.

the orange wire runs to your dash instrument cluster (goes through light bulb) and from there a brown wire (brn-25) runs to the alternator.

See attachments.- for clarification

 

[blackbird454]

It's power comes through (sort of) the heater fan switch (at least the wire running to the switch). On a 77 there will be a brown wire (brn-50) feeding the heater switch but an orange wire (orn-939) comes out of a connector on the way into the switch. That orange wire feeds the exciter. Depending the heater issue- check the heater fuse. (same fuse the exciter uses). Then check the connection I mentioned above.

the orange wire runs to your dash instrument cluster (goes through light bulb) and from there a brown wire (brn-25) runs to the alternator.

See attachments.- for clarification

Brother you may have solved my issue there is no fuse in the heater bank someone (before me) cut the heater wire that feeds 12v to the heater so I’ll stick a fuse in the heater portion thank you so much

 

[blackbird454]

You can run a socket and light bulb 1 end of the socket to any keyed 12v source other end of socket to alternator terminal 1 it will work just like the dash light but it will be where ever you put it. Have you checked your dash bulb?. If you are super lazy you can hook a buzzer or moped horn to terminal 1 and to keyed source under the hood. You turn the key,you hear the buzzer,you know your circuit is good the truck starts the buzzer quits you know you are charging

I’m just curious if I can just run a switched source to the terminal 1 or if it will back feed I’m ok with feeding it 12v’s lol I do care about to ol girl though so I’m trying to treat it right

 

[Ricko1966]

I’m just curious if I can just run a switched source to the terminal 1 or if it will back feed I’m ok with feeding it 12v’s lol I do care about to ol girl though so I’m trying to treat it right

Run a switched source through a light bulb to terminal 1.

 

[blackbird454]

Run a switched source through a light bulb to terminal 1.

Does it matter if the light bulb is grounded? I have a 2 inch temp gauge pod inside I don’t have the light wired up because I can see it I would use that if you see no issues I posted a picture of the gauge below

 

[blackbird454]

It's power comes through (sort of) the heater fan switch (at least the wire running to the switch). On a 77 there will be a brown wire (brn-50) feeding the heater switch but an orange wire (orn-939) comes out of a connector on the way into the switch. That orange wire feeds the exciter. Depending the heater issue- check the heater fuse. (same fuse the exciter uses). Then check the connection I mentioned above.

the orange wire runs to your dash instrument cluster (goes through light bulb) and from there a brown wire (brn-25) runs to the alternator.

See attachments.- for clarification

Well I stuck a fuse in heater fuse slot no go still didn’t illuminate the gen light I’ll check more after work but I believe the climate control switch isn’t doing the best so I’ll check the connections behind it too

 

[Ricko1966]

The alternator term 1 is the ground. Wire to keyed source to light bulb,wire from light bulb to terminal 1. Power goes through the wire through the light bulb through the other wire grounds on terminal 1 at the alternator through the windings. Which excites the alternator.

 

[blackbird454]

The alternator term 1 is the ground. Wire to keyed source to light bulb,wire from light bulb to terminal 1. Power goes through the wire through the light bulb through the other wire grounds on terminal 1 at the alternator through the windings. Which excites the alternator.

Yeah I think I am over thinking it I wasn’t sure if I wire the keyed portion to the red wire on the light bulb then the black wire from the bulb to the terminal 1# but if I am understanding you correctly I wire the switched power to the light bulbs red wire then jump off the same red wire to the terminal one sort of in series correct? I seen some folks use a bulb that didn’t appear to have a ground that gauge bulb does so I just wasn’t sure on how that plays out lol. My question is do I run the ground wire from the light to terminal 1 or the positive wire from the light to terminal 1 thank you again

 

[Ricko1966]

Yeah I think I am over thinking it I wasn’t sure if I wire the keyed portion to the red wire on the light bulb then the black wire from the bulb to the terminal 1# but if I am understanding you correctly I wire the switched power to the light bulbs red wire then jump off the same red wire to the terminal one sort of in series correct? I seen some folks use a bulb that didn’t appear to have a ground that gauge bulb does so I just wasn’t sure on how that plays out lol. My question is do I run the ground wire from the light to terminal 1 or the positive wire from the light to terminal 1 thank you again.

A light bulb has to have 2 connections 1 connection goes to power,the other connection goes to term 1. Look at the light bulb in the picture. Your alternator should be marked terminal 1 and terminal 2 in this pic 1 is 1 b is 2. Verify the position of 1 and 2 on your alternator. This is a generic alternator drawing.

 

[blackbird454]

Yeah I think I am over thinking it I wasn’t sure if I wire the keyed portion to the red wire on the light bulb then the black wire from the bulb to the terminal 1# but if I am understanding you correctly I wire the switched power to the light bulbs red wire then jump off the same red wire to the terminal one sort of in series correct?

A light bulb has to have 2 connections 1 connection goes to power,the other connection goes to term 1. Look at the light bulb in the picture.

You must be registered for see images attach

Right I completely understand that however I understand I run 12v to the red wire (positive) of the light bulb that leaves the ground wire do I connect the ground to terminal one or the (positive) wire the terminal one

 

[Ricko1966]

Right I completely understand that however I understand I run 12v to the red wire (positive) of the light bulb that leaves the ground wire do I connect the ground to terminal one or the (positive) wire the terminal one

Look at the pic red is + yellow is negative.

 

[blackbird454]

I think I understand now you run 12v to the hot wire of the bulb and the ground to the terminal 1 alternator is the ground until it is excited essentially once that happens it loses the ground lights goes out

 

[Jgonick]

also-- check your light bulb in dash for gen/alt- If that light bulb is burnt out it could also be the issue. Like Ricko1966 pointed out- 12v source through light bulb to terminal on alt -which acts as ground- Light comes on. Once alternator starts alternator feeds 12v back up the wire (Think of garden hose with water being fed into both ends- the water doesn't flow)- so since the light bulb is being fed 12v from both directions it will not light up (electricity not flowing)

Edited - @blackbird454 ,you posted when I was typing- Yes, you got it....