Low voltage on low beam

[MrGreen]

1980 spider 2000
I turn on lights and right low beam does not work. Left low beam and both brights work. Changed the bulb still no good. Put a multimeter on and get ~10.4 volts out of green wire (high beam) but only 8+ off grey. Tried it off the connector direct to the wire and had same result. Wire looks ok as it courses through engine compartment. Will a bad fuse still pass current but not enough?

[spider2081]

Did you measure the voltage on one side of the fuse and then the other. The right side lo beam fuse should be fuse F or 6th fuse counting from the steering column. THe fuse itself is not as likely to be the problem as the connections for for the fuse.

[GeorgeT]

Install headlight relays. As it comes from the factory, the circuit for the lights goes through the ignition switch, through the dash switch and then through the high/low switch on the column and there is a significant loss. Relays eliminates all of this while maintaining all the switches functionality plus the lights are much brighter.

[MrGreen]

Thanks but still lost
Right fuse looked bad. Stole the one from the left but did not work on the right. Sanded the slot clean and still not. Meter measures around 50mV on both right and left when lights are on. Both go to solid 0V when shift to brights. Double checked meter integrity on a lab voltage generator. Have no info from previous owner, bought from a guy who flips old cars. Should I be looking for a relay somewhere?

[spider2081]

Usually when relays are installed they are installed after the fuses. The voltage on the fuse activates the relay so you would still look for voltage on the fuse. They could be wire different but that would be unusual. Did the left headlight lo beam light with 50 mv on its fuse? From memory I think the top of fuses 5 and 6 are connected to the lo beam switch. So both should measure battery voltage with the hi/lo switch in the lo position and the head light and ignition switches on. Headlight switch usually down is on.

[GeorgeT]

Usually when relays are installed they are installed after the fuses.

I installed my relays with in-line fuses directly off the alternator (the same stud that is connected to the battery). The only power going through the original fuses was to activate the relays; very low amps.

[spider2081]

That is what I was trying to say your relays are after the factory fuses. If there is no power to the original fuses your relays will not energize. Mrgreen needs to find out if the original fuses have correct voltage fed to them. From there he can either fix the system as Fiat designed it or add the Headlight relay circuit if it is to be wired the most common way.

[spider2081]

This post had me wondering what fails in the column switch assembly. I had one that I changed because the hi beams stopped working and I took it apart last night. What I found is the stationary part of the contacts is a hollow rivet that holds the wires ring terminal against the plastic base. The ring terminal becomes loose over time and makes a poor connection to the rivet/contact. The resistance is enough to keep the headlights from lighting.

There is a great possibility installing headlight relays would bypass this problem. So before changing a column switch assembly I would try the following test.

1. Disconnect both the drivers and passengers side 2 pin plug that feeds the headlight buckets. They are located on the inner fender wells. One pin is lo beam and one is hi beam voltage to the bucket.

2. Measure the voltage (both hi beam and lo beam) on the cars side of the connector. It should be very close to the batteries voltage on all 4 pins. if it is not check the fuses.

3. Reconnect the headlight bucket connectors so that a small portion of the pins show. Measure the voltage again on the pins.

If you have correct voltage with the buckets disconnected but it is much less with them connected adding the relay circuit will most likely fix the headlights even though the column switches have poor connections.

The original Fiat circuit is used to control the relays so this circuit has to be complete meaning no broken wires or blown fuses for the it to energize the relays. Usually the drivers side of the original circuit is used to control the relays. One relay controls both hi beams and one controls both lo beams.

Hope this helps someone

So this showed me adding the relays is a good idea because it extends the life of the column switches as well as giving brighter headlights.

[seabeelt]

I would go back to the fuse box first. To test the colum switch, check the voltage at the blue and the gray/red wires coming from the colum switch into fuses 3 and 5 respectively. One is low beam, the other is high beam.You should have 12 or so volts. I would do this with the headlights disconnected at the fender wells as previously described. If you don't have 12 volts, you need to look at the column switch. If you have 12 volts check the output of fuses 3 and 4 ( green and green/black) and fuses 5and 6 (gray and gray/black). If you don't have 12 volts, on the output side, check the fuses. Each head light has a fuse for the high and low beams ( four fuses total) also check the wire connections to the fuse box, both sides, clean if necessary and make sure they fit tightly. If you have 12 volts both sides, then check the continuity of the low beam wire. Should read next to nothing in terms of ohms. If more than that you have a partially broken wire. Check the connector where it pugs into the headlight pigtail. Check the grounds on the fender wells. This is a pretty simple circuit. Ignition switch to headlight switch to column switch to fuse box to headlights. Nothing else inbetweent unless added by a PO.

I ran relays from battery to headlight using the column switch as the turn the relay on signal. One wire from the battery to the relays, one wire from each relay to fuse 3 and 5 and took the blue and gray/red wires from the column switch to trigger the relay. Big improvement in direct power and big improvement in reducing ignition switch, headlight switch and column switch fatigue.

[MrGreen]

Solved
Thanks for all the advice. Work got in the way of car time and tonight I had at it. I trimmed back the wires at the connector to the bulb. Sanded them shiny and put in a new connector. Works so far.