I can hear the turn signal in the fuel pump

[Johnnyb]

The fuel pump is wired from the battery fused through a relay and then to the pump.
The alternator is 4G with a standard fusible link to the battery.
I can turn on the headlights and every other accessory in the vehicle and watch the voltage hold steady above 14V.
When I turn on the turn signals however the voltage fluctuates about 2/10 of a volt when the signals flash and I can hear it in the fuel pump.
Would this be considered normal or is it a failure of the alternator to react quickly enough to the load caused by the turn signals?

THX,
JB

 

[tutone]

I wouldn't think that is a failure of the alternator, but maybe you have the flasher or wiring pulling down the voltage more than it should? .2 volts isn't a lot but seems excessive for that. If it happens on both left/right, I'd suspect the wiring to the flasher. Maybe do a voltage drop test? Maybe you have a weak ground wire somewhere.

 

[Oldtimer]

Is fuel pump in (near) tank?
I would suspect ground issues between tank/pump and frame, and rear turn signals and body/frame.
The only factory ground between frame and body on early models was the ground wire from tank sender to the body/frame.

 

[Johnnyb]

Since the turn signals are through the painless harness, and the fuel pump is basically wired from the battery I was not thinking ground issues but I'll check.
Other accessories come on and the voltage drops but recovers immediately, the turn signals are intermittent and I was wondering about that?

 

[Broncobowsher]

Headlights are a bigger load than turn signals.
The late model alternator recovery time is crazy fast, few milliseconds.
Do the hazards also cause the voltage dip? What about hazards and brakes together (that bypasses the flasher and keeps all the turn signals on continously, at least with the in dash hazard switch)

You may be seeing a 0.2V drop with the signals on, but does the alternator really drop that much? Do you get that drop between the sense wire (the one that should go to the battery but most people just loop to the alternator output) and the alternator case? If so, well the alterantor really isn't keeping up with the turn signals, which would be weird. It does? Start looking for the 0.2V drop. Is it on the ground side? alternator case to battery negative post. I keep going to the alternator case as the ground reference as that is where the voltage regulator sees ground at. So also alternator case to body, engine block, etc. And the positive side as well. Where is that 0.2V drop happening at? And it may not all be in one place. Might be a fraction here and a fraction there. But it will all add up. Time consuming with a lot of dead ends. But that is the game with electrical diagnostic work.

 

[Johnnyb]

@Broncobowsher , I will do some checking around and post back here.

 

[73azbronco]

welcome to analog age. Pretty normal if you ask me, but check ground for fuel pump. Old school bulbs? Yeah, normal.

 

[MarsChariot]

What 73azbronco said. I have another vehicle with an electric fuel pump. Before I went to all LED lights, the turn signal flasher would change the pitch on the fuel pump in time with the flasher. Fairly normal but nothing worrisome.