changing pitch in fuel pump noise

[micbrody]

Fiat 2000 1981. I just purchased it. Fuel pump work; and I can here the hum. However, the frequency (musical pitch) changes when head lights on; and especially with on/off of turn indicator. Any thoughts?

[4uall]

I would start a band

[majicwrench]

I can play along with my harmonica!

Obviously the voltage to the pump changes. If you are idling when this happens is probably no big deal, anything that loads to system is gonna change the volt a bit at idle.
Might be fun to hook a volt meter into pump power wire and compare that to battery voltage.

[micbrody]

I have figured out the issue. Previous owner had bypassed double relay fuel pump power source by splicing directly into fuse 1 location which also powers brake lights and turn indicators.
I found the cut end of original fuel pump wire that goes to double relay. I started car (in accessories position, no fuel pump sound) and it started right away.

After feeling good about my accomplishment, I started thinking why would PO bypass double relay if car started easily. I got back into car, and tried starting it again.......this time no luck. Car would not turn over.

I removed double relay; disassembled housing. Tested the magnets; they worked. I checked the circuits that were suppose to close when magnet energized. One of the connections was very flaky, requiring a tremendous amount of extra force to make continuity. I sanded the contacts and sprayed with deoxy multiple times........still very flaky continuity. I then discovered that the actual contacts were fine; but one of the contacts belongs to a flat piece of copper that rests and pivots on another piece of copper. This connection was the culprit. I deoxyed the pivot points (2 for each relay) and put a very light coat of copper anti-seize compound. Now relays work great. Car starts immediately.

[4uall]

https://www.youtube.com/watch?v=3GwjfUFyY6M