Vacuum gauge indicator light?

[amishbuggy]

I have a vac gauge that I got out of a 600 panel and I'm wondering about the indicator light. Is it for shifting or a warning light? If it's for shifting what sort of solenoid would I need to make it function?

Thanks alot
Pat

[Thunderfoot]

Some of these were for Low Air Pressure for the air brake trucks, or possibly low vacuum for vacuum assist brakes... The light is just that, a Light, and you can use it for anything you want all it takes is a grounding switch/signal to make it light. Is should have power to it from the instrument panel but if not then would need to put power to it.

[amishbuggy]

Thanks, I'll just leave it dead. I was thinking it might have something to do with fuel economy or performance although with the hugh face I don't know what good a little light would do.

[Thunderfoot]

Back then Fuel economy wasn't much of a thought.

[amishbuggy]

Yeah I know, I'm just thinking out loud. Whatever the light is for it just does'nt seem to make much sense with the size of the gauge itself. I know in big trucks the low air warning light and buzzer is useful because the gauges are small and now that I think about it I don't remember any of the Pete's or KW's I drove with a vacuum warning light or buzzer, but I've been wrong once before.

[Mancar1]

I have owned two 65 Cudas. They had vac gages. I would think the light is just to illuminate the gage face at night. Vac gage will help with your fuel economy if you pay attention to the reading and accordingly. But thats no fun.

[amishbuggy]

This one has a light for illumination and this second light that has a red lense at the bottom of the face plate. I have a vac gauge in my truck and I always watch it to try and and keep the vac as high as possible, that's why I was thinking that the light had to do with the whole shifting thing. My '02 Jetta has a shift light on the dash for maximizing economy, I'm not sure if that is triggered by vac or rpm's or something different.

[cep62]

I have a vac gauge that I got out of a 600 panel

Was it an old U Haul ?
I have a '78 F350 U Haul that has a low fuel economy light.
It's not hooked up but I would think it's triggered by vacuum.

[knightfire83]

The dents do have a low fuel economy light in the dash. It is triggered by a little switch on the firewall that is connected to manifold vacuum.

[amishbuggy]

Thanks for the pic, now I'll just have to find a switch.

[Hawkrod]

I have not looked into that in a while but I seem to remember that all 75's had that light and maybe 76's as well. It was a short lived thing on regular trucks but is very common on fleet trucks. Hawkrod

[70_F100]

That light is a "Low Vacuum Warning" light.

The gauge measured vacuum in the vacuum reservoir for the brakes (hydrovac system).

IIRC, the light was set to come on at about 10-12 InHg to warn the driver that the vacuum assist for the brakes had a low vacuum condition. It was similar to a "Low Air Pressure" alarm on a truck with air brakes, which I know for a fact came on at 90PSI.

[steveh]

I used my as a Alt light after i did some changing to the charging system wiring as the AMP meter on the dash is more that just useless!!! I used a two wire socket instead of the one that came with the gauge. Like some else mentioned - You can use it for anything you want.

Steve

[Bullitt390]

That light is a "Low Vacuum Warning" light.

The gauge measured vacuum in the vacuum reservoir for the brakes (hydrovac system).

IIRC, the light was set to come on at about 10-12 InHg to warn the driver that the vacuum assist for the brakes had a low vacuum condition. It was similar to a "Low Air Pressure" alarm on a truck with air brakes, which I know for a fact came on at 90PSI.

The warning light or Buzzer will be active until the system builds 60 psi. The governor should cut-out at 125 psi. If the system builds more than 150, the safety valve should release.

Josh

[70_F100]

That light is a "Low Vacuum Warning" light.

The gauge measured vacuum in the vacuum reservoir for the brakes (hydrovac system).

IIRC, the light was set to come on at about 10-12 InHg to warn the driver that the vacuum assist for the brakes had a low vacuum condition. It was similar to a "Low Air Pressure" alarm on a truck with air brakes, which I know for a fact came on at 90PSI.

The warning light or Buzzer will be active until the system builds 60 psi. The governor should cut-out at 125 psi. If the system builds more than 150, the safety valve should release.

Josh

I stand corrected. The correct air pressure for the warning light and buzzer is 60 PSI on trucks equipped with air brakes. The rest of your information is correct, also.

Keep in mind, though, that that is for air brakes, not for the vacuum gauge the OP asked about. The information I posted about that is correct.

It's been about 20 years since I was a truck technician, and I'm probably in the late stages of Hafzheimers...