Intermittent No Charge

A few days ago after I started my truck, I noticed the dash lights and headlights were a bit dim and the window was rolling up very slowly. I switched my head unit to the vehicle information display and it showed only 11.6 volts. While I was contemplating getting my truck all the way home at night with no charge, the lights suddenly went bright and the voltage jumped to 13.8. At this point I was thinking a failing alternator.

This morning, after dropping off my kids at daycare, the same thing happened, only this time I also noticed that my fog lights weren't coming on (they may have not been on the first time, just didn't take notice). I pulled over and with the engine running, popped the hood and gave a sharp slap to the fuse/relay box. The fog lights instantly came on, headlights brightened, and voltage bumped back up to 13.8.

With this information, what relay should I be looking at that is loose or failing and could cause the truck to start and run but not accept a charge? At no point has a check engine light or battery light come on.

 

Definitely on the list to check the engine and chassis grounds once I get home. The battery terminals are freshly cleaned and tightened and the battery is only a month old so it's not those.

 

I would fully charge my battery with an external charger first and then go to an auto parts or battery store and have the battery and charging system tested. Most stores will do this at no cost. The vehicle's charging system and battery are co-dependent on each other and both must be healthy. Terminal corrosion and low electrolyte levels are very common causes of undercharging.

 

The battery is brand new, and I suspect this issue was occurring before I replaced the battery.

 

This issue is on my personal Tacoma, not the work one, so no extra loaded gear. I'll keep my eye on this on the patrol truck.

As it turns out, there is a relay in the under-hood relay/fuse block that specifically deals with battery charging. While not really loose, I did push it down harder and wiggled it a little to knock away any corrosion. I still haven't had the time to pull it into my shop and go over all the connections with a fine tooth comb, but I think I know where to start now.

 

Which specific relay do you suspect?

Electro-mechanical connections are always the first suspect when intermittents are involved, for example, starter solenoid contacts.

 

After a year of just dealing with the issue, it's frequency increased to the point of frustration, so I dug into the problem. I discovered that the pictured plug (with yellow/green wire) was quite loose even though it was fully seated in its socket. I wedged a small shim in between the plug and socket and the problem has gone away. Thought I'd post my solution in case anyone else has this issue.

 

I am glad you isolated the intermittent connection. What is with the heavier blue wire stuck in with the green wire and appeared to be glued into the plug? Can the two wires be solder spliced and insulated for a better electrical connection?

 

That is where I tapped power for the fog light mod. I removed the pin and soldered it all together before putting the pin back in, but there was still a lot of exposed wire so I used conductive carbon glue to seal the rest.