New wiring harness, new factory headlight switch x3, new high beam dimmer x2, new voltage gauge (Bosch) x3. New snowplow transfer light switch x2. New 130 amp alternator x3.

With headlights on, it draws the RPMs down and at the gauge, it only reads 12 volts but putting out 14 volts at the alternator and batteries. Headlights are bright, so I’m guessing it’s not a ground issue…or is it?

**It DID NOT DO THIS BEFORE. Has always been Rock solid 14V at the gauge and no RPM fluctuations with headlights or plowlights on up until recently. The switch and wiring feels warm to the touch, but not hot.

I have hundreds of dollars in replacing good parts multiple times, and I would chalk it up to just getting a bad gauge a few times, but it doesn’t explain the big drop in RPMs when switched on.

-a real head scratcher. Any ideas?

thank you

 

Well the RPM coming down is because of the load and you are only checking voltage, what amps are the head lights and other lights pulling is the question?
You hinted about grounds but I dont think you pulled all of them to clean the connections?
Battery to motor, motor to frame (heavy cable), motor to cab heavy ga. wire 10ga) and would not hurt to run a 10ga wire from frame to bed.
You can never have enough grounds!

Wires feeling hot means there is a lot of load (amps) going through them and that is not good.
Over time the wire resistance goes up also that adds to the heat.
I did not read anything about a head light relay kit installed?
This pulls the load off the wiring and switch and the load is pulled from the battery, switch & wiring is only used to switch the relay on & off.
If you have plow liths you may want to do a relay kit on them too.
If you think the lights a bright now just wait and see with the relays..

BTW when does the RPM drop when the light are turned on just after you start the motor or after you been driving it so the battery had time to recharge and then turn the light on?
I run a relay kit on my 81 F100 and the only time the head lights go dim at idle is right after I start the motor and back out of the garage. Once the battery has had time to recharge from starting no more dimming at idle.
Dave ----

 

A basic stock bulb use the following current.

Bulb Family: C6
Color: Clear
Voltage (V): 12.8 Volt
Wattage (W): 35, 65 Watt
Amperage (A): 2.73, 5.07 Amp
Base Type: 3 Contact Lugs

it would seem fairly obvious that you are not using standard bulbs

as mentioned already, you need to be using relays to power the headlights directly off the battery.

jim

 

You would ned to x2 of the watts / amps as the truck has 2 bulbs.
But yes on the relays. LMC, JBGY and think you can find them on EBay
Dave ----