leeklm

Getting the 79 headlights almost working... Primary issue were the under hood relays. Now, when pulling the light switch, the headlights do not move - but they will come up when pulling the over ride switch down.

The lights will continue to stay up (with light switch on), and will stay up, even after pressing the over ride back up (again, with the light switch still on).

Now when shutting the light switch off (with over ride up/off), the lights go back down as they should.

It seems that maybe the light switch is bleeding air when pulling it on, and not letting enough vacuum through to activate the relays?

Any thoughts before I pull the switch out of dash to properly test it?

Thank you!

0Willcox Corvette

Are you sure you have the hoses on the switch in the correct position. There was a diagram that floated around by a disgruntled fool that had the hoses on the headlamp switch backwards. He thought it was a funny way to trip up people that purchased his hoses from another zippy vendor.

So if I were you the first thing I'd do is double check your hoses at the headlamp switch.
Here is the correct schematic and you can have it, distribute it or do what ever you want with it.. it's free..

Then I'd make sure the headlamp switch is blocking vacuum when the switch is pulled in the on position...

If you need more help, post back..

Willcox

Dave J

Classic case of switched headlight vacuum hoses. The vacuum source hose ALWAYS goes to the port closest to the pull ****. If you are unsure, and before you pull the dash apart, there is a way of testing that does not involve pulling the dash.

1 - pull the override **** out, blocking the circuit.
2 - connect vacuum pump to the small hose at the check valve
3 - pump it up, correct readings test as;
3a - **** pushed in, should hold vacuum
3b - **** pulled out, should hold vacuum
4 - switched hoses would test as;
4a - **** pushed in, should hold vacuum
4b - **** pulled out, does not hold vacuum

The reason is the port farthest from the **** vents vacuum when the **** is pulled out, and the closest port blocks it.

Peterbuilt

leeklm

Thank you for the replies. When testing the switch, I was generally getting the correct readings, but was leaking some vacuum. Disassembled the switch plunher, cleaned and reinstall, tightening down the friction seal around the rubber plunger. The lights now work!!! Thanks again for the tips.

In the end,
​​​​I was fighting two separate issues, the underhood relays and a leaking light switch.

Peterbuilt