69 F100 headlight issues

[Danielg_84]

Hello all, first post.

Trying to get my new-to-me 69 F100 ready for inspection, and I have 2 headlight issues.

1) I need to install a dimmer switch. There currently isn't one. A previous owner apparently removed the switch, cut the connector clip, and connected all of the individual wires. So, I've ordered a new switch and connector, and will likely be back later if I can't figure out how to wire in the connector.

2) Good chance the problems are connected, but the headlights seem to have a bad connection somewhere as they cut off and back on randomly, especially in wet weather. Any ideas for likely culprit?

I'm a decent mechanic, but electrical stuff is definitely not my wheelhouse. Hoping I can avoid pulling the dash.

Any help appreciated!

[Nitekruizer]

'69s are cool trucks.

Some POs do some strange things. The problem is that by having your Low Beam and High Beam filaments lit at the same time, your Headlight Switch is being overloaded and will eventually fry. There's a circuit breaker in the switch itself and that is what is making the lights go on and off intermittently. You have to have the floor dimmer switch. There not too difficult to wire in.

[Danielg_84]

Thanks! It sounds like that means replacing the dimmer switch should fix the problem, if I understand you correctly.

[Danielg_84]

Installed a new dimmer switch last night and solved the enigma of the PO's headlight and turn signal wiring. Everything worked fine. I get in to drive to work this morning, and poof...no low beams. Only the high beams are functioning, and they're cutting in and out randomly.

I found a relatively inexpensive wiring system and I'm toying with the idea of ordering it and spending a weekend just rewiring the whole stinking truck. I cant stand messing with electrical stuff, and I'd rather just knock it all out in one go and not have to deal with it for a while.

[Canonman67]

'69s are cool trucks.

There's a circuit breaker in the switch itself and that is what is making the lights go on and off intermittently.

I would try replacing the headlight switch first.

[Danielg_84]

'69s are cool trucks.

There's a circuit breaker in the switch itself and that is what is making the lights go on and off intermittently.

I would try replacing the headlight switch first.

Ordered! Thanks!

[Nitekruizer]

It sounds to me like there is still a problem with the wiring, probably in the dimmer switch circuit. The power for the headlights comes from the Headlight Switch to the floor mounted dimmer switch, then to the bulbs. If your high beams are cycling "on" and "off" because of a defective Headlight Switch, then your low beams should still work, but may cycle "on" and "off" too. In other words, a defective Headlight Switch wouldn't cause the low beams to not work at all, while still allowing the high beams to work, unless there's a short in the system or it's wired wrong.

I wouldn't necessarily order or install a new wiring harness, but you may want to consider installing Headlight Relays. However, even the relays won't likely solve your issues unless you find the problem with the present circuit.

[Danielg_84]

Installed a new headlight switch and it looks like everything is working properly. Hoping it doesn't come back! The re-wire project isn't just because of this issue. The wiring is pretty cluster-beeped throughout.

[Danielg_84]

Wrote that last post in a hurry...here's the full story. The dimmer switch and the headlight switch were both faulty, AND the PO had installed relays. However, he managed to install the relays in parallel to the original circuit, including a new fuse on the relay circuit.

Replaced the switches and rewired the circuit...problem solved! Finally passed inspection 3 weeks after bringing the truck home!

Thanks for the help!

I'll probably grab some LEDs in the future and go back to the original circuit for simplicity's sake.

[Canonman67]

Glad everything worked out. Electrical gremlins are guaranteed to drive you crazy, especially when someone else has screwed around with it first.