Generator 1 light on

[jmsneorrcom]

84 M1009 - would not start so I replace all the battery cables(started right up) - now the Generator 1 light is on - batterys are fully charged and it seems the alternator is charging - any Ideas? - thanks

 

[Barrman]

Do a test on each battery with a digital volt meter and then post what you find with the engine running.

 

[edmorgan099]

also have this problem

i was wondering if both batteries should read well over 12 volts while the engine is running, my rear battery showed about 15 on the volt meter and the front showed 12.6, about the same as when the truck is not running.

 

[Barrman]

12.6 volts is a fully charged battery at rest. 14.4 volts is what each battery should show when the truck is running and the alternator is working. Depending on how you measure, you might get 12.0-14.4 on one battery and 26.4-28.8 on the other. 28.8 across both is considered the goal by the way. Sounds like you have a charging system in need of help.

 

[azex]

I've got a similar issue with my M1008. We had another M1008 to compare it too and all the wiring looked identical.

However, my rear battery, shows 26.6v, as does the passenger side Alternator, EVEN WHEN NOT RUNNING. While the other battery shows 14 or so, and the driver side Alternator shows the same.

Very weird. I had a battery blow up last July 4, just KABOOM, and the top was blown off, if it's getting 26.6v all the time, isn't this bad and won't it contribute to the battery cooking dry and going bad?

How about that other truck? Why did it test front battery:14, rear battery 14?

 

[SGT Estum]

I've got the same (or similar) problem, so I just happen to have the -20 TM open to the troubleshooting section.

From page 2-59:

6. GENERATOR LIGHT REMAINS ON OR TURNS ON DURING OPERATION (ALL EXCEPT M1010)
Step 1. Check engine idle speed. (See paragraph 3-25)
Step 2. Disconnect connector from left alternator (if “GEN 1“ light is on) or right alternator (if
“GEN 2“ light is on). Turn key to “RUN” position.
If generator light is not on, trace circuit from alternator connector to generator
Iight in instrument panel. (See wiring diagram F-11) If circuit is good, replace
alternator. (See paragraph 4-2)
If generator light is on, trace circuit from alternator connector to generator light
if instrument panel. (See wiring diagram F-9)

 

[mtn man]

do the 'shade tree test' swap the alternators and see if Gen 2 light is on... if so its the alternator that has decided it didn't want to play anymore. If the gen 1 light remains on you can began the wiring fun. been there done that... but as you know this site is a great source of endless help good luck

 

[1stSarge]

do the 'shade tree test' swap the alternators and see if Gen 2 light is on... if so its the alternator that has decided it didn't want to play anymore. If the gen 1 light remains on you can began the wiring fun. been there done that... but as you know this site is a great source of endless help good luck

“Field Expedient Fault Isolation”

 

[doghead]

FEFI (aka, feefee test!)

 

[jmsneorrcom]

front battery is 11.4 off and 10.4 when running
back battery is 13.2 off and 14.4 when running

 

[jmsneorrcom]

on the firewall directly behind the driver side alternator where the battery cable runs along the firewall. there is a cluster of wires. they are blue go into a black connector and then are red. the black connector, do those come apart there?

 

[Warthog]

on the firewall directly behind the driver side alternator where the battery cable runs along the firewall. there is a cluster of wires. they are blue go into a black connector and then are red. the black connector, do those come apart there?

The black connectors are sealed and have to be cut off. They connect the regular wire to the short piece of fusable link wire.

When I need to replace a fusible link, I cut the wire right behind the black connector and use a butt splice connector to attach the link. I cover the connector with shrink tube. There are many youtubes showing how to do this.

 

[jmsneorrcom]

The black connectors are sealed and have to be cut off. They connect the regular wire to the short piece of fusable link wire.

When I need to replace a fusible link, I cut the wire right behind the black connector and use a butt splice connector to attach the link. I cover the connector with shrink tube. There are many youtubes showing how to do this.

so the blue wire is the fusible link? if not how do you know what the link looks like

 

[jmsneorrcom]

there is a 1989 CHEVROLET SUBURBAN at pull apart in cleveland, are there parts compatible with the M1009?

 

[SGT Estum]

so the blue wire is the fusible link? if not how do you know what the link looks like

Yes, the blue wire is the fusible link. There are actually 3 fusible links that go to that same terminal on the firewall. You should check all three of them to see if any are blown/melted.