So for some reason I felt the need to buy a 1988 F-150 with a 302 V8 5.0L about three years ago and fell in love with it. Well, recently I've run into some electrical issues. If I turn on all or most of the electronics like windshield wipers and sprayers, headlights, and the blower fan, the truck begins to buck like crazy. Also, if i have some electronics on and I'm waiting at a light or just at a stop, the blinker will begin to slowly stop blinking and eventually stop. I figured I had a low voltage problem and my first thought was battery or alternator so naturally I checked the voltage at the battery, first with nothing on and got a reading of 14.5V, which seems a bit high but the opposite of what I believe to be the problem. Then, I replicated the no blink situation and got a reading of 12.5V both when I tested the battery posts and when I touched the positive post and the alternator case. That should be enough to run the electronics but I still have the problem. So I took out the flasher and used my multimeter to test the voltage at the fuse box and got 11.4V. That's as far as I've gotten because it doesn't seem to only affect the blinker but also the running of the vehicle so I don't want to pursue the blinker. The issue seems to affect the whole electrical system and I'm at a loss. Any feedback would be much appreciated or even a wiring diagram.

 

Missing, loose, or corroded ground cables, wires and connections. Very common with a few trips around the block. Buy new ground and start cables, they had a good run but they are done by now. All that resistance will eventually smoke the alternator/voltage regulator. 14.5 from alternator is what you want to see, but the current needs to be able to get there too. Clean, bright, tight electrical connections = Happy Electrons

Welcome to FTE btw.

 

Thank you for the welcome lol. I appreciate the input, my only thing is that I tested the main ground and had 12.5V when I put my probe to the positive terminal and the negative probe to the alternator casing to test if the ground was screwy. So, I took a separate length of wire and ran my own ground to my voltmeter and still got the 11.4V at the fuse panel under the dash. I'm still going to clean and probably replace the main ground but it seems to be something more like a corroded hot wire. Any ideas on where I should start looking? Any wires that corrode/cause more problems than others?

 

Since it affects everything it's got to be a major drop. The tell is when you load up the system by turning all that stuff on. There are three main ground bus connections. Battery to block or maybe a bolt on the starter, block to frame, and block to firewall. All three are important or they wouldn't have put them there. Auto manufacturers are cheapskates when it comes to wire! Positive cables to solenoid, solenoid to starter etc. Grind down the connection points on block frame and firewall to bright shiny metal and tighten securely. If the cables are thirty years old they are done.

If you want to try and narrow it down and really see where the voltage is being lost. Set your voltmeter on the lowest setting. Place one probe on the negative battery terminal. Turn on the headlights and heater blower like you did before. Spool up the RPM to maybe 2000 or so. Place the other probe on the alternator case. Since voltage will seek the the easiest path the voltage being lost in the entire ground circuit will be displayed as a positive voltage. More than 0.10th of a volt is considered excessive. Can do the same test on the positive side, should not exceed 0.3 volt. Also can narrow it down and check voltage drop of individual wires, cables or connections, for example even a battery post to the terminal itself. The circuit has to be under load for this type of test, but it's quick and easy and doesn't require disconnecting anything. Works for headlights, and starter system during cranking as well. Let us know what you find.