Gen 1 Light & heater control

[carter262]

This is odd so I was wondering if any of you have seen this before.

I have noticed that sometimes my Gen 1 light is glowing dimly. You can only see it when it is dark out. You can not see it on sunny day. This morning I made the connection to when it is doing this. It was raining and cool this morning so I cut the heat / defrost on. I noticed that the Gen light was glowing dimly again. Then I cut the defrost up to high and the Gen 1 light got brighter. So I cut the defrost down to low and the Gen 1 light got dimmer. So with my powers of deduction I have determined that for some reason when the heat is on it is making the Gen 1 light glow / activate.

I have checked the output of the alternator and it is fine.

This vehicle is a 1987 M1028. I have a 1984 M1009 too and it does not do this.

So what could the cause be?

 

[ehuppert]

I'll be watching this one! Mine has done this for the ten plus years i've had it... Always charges, but light dimly glows with heater on!

 

[cucvrus]

That is the diode in the alternator. I had this issue fixed at the alternator shop. He installed a relay somewhere in that wire for the blower switch. I will ask him. At the same time he set up the alternators so they charged without the idoit lights operational. It was a plow truck and I had a nightmare of issues with it 2 winters ago. It is coming back to me when I am finished with the M1009 plow truck for repairs to the steering. JOY. So I have that to look forward to. Which is good. Take Care.

 

[Barrman]

I gets spooky when you leave the fan on and turn off the engine. The light will slowly dim as the fan motor spins down.

most of my Gen 1 lights have done this. But not all.

 

[ehuppert]

The glow has persisted with several different alternators over the years. Only visible at night, and being a "work" truck it doesn't get driven at night very often! This is not a 6.2, so is fully converted to 12v with a 10si alternator on a small block!

 

[carter262]

That is the diode in the alternator. I had this issue fixed at the alternator shop. He installed a relay somewhere in that wire for the blower switch. I will ask him. At the same time he set up the alternators so they charged without the idoit lights operational. It was a plow truck and I had a nightmare of issues with it 2 winters ago. It is coming back to me when I am finished with the M1009 plow truck for repairs to the steering. JOY. So I have that to look forward to. Which is good. Take Care.

Thanks. Please let us know if you find out more.