I drive a 2001 GMC Sonoma SLS. It has 138,000 miles.
For the last year, I have discovered an interesting problem. It only happens when I am driving the truck in wet conditions (i.e. when it’s raining).
If I’m driving down the road on a rainy evening, every so often, my electrical system starts to struggle. My instrument cluster and headlights will dim significantly, and my defogger fan’s speed reduces significantly. This drop in power can last anywhere from 10 - 15 seconds. Then, everything comes back to full power.
During these lapses, the engine will continue to run normally. The electrical gauge in my instrument cluster shows a drop in charge when this happens.
I’ve managed to avoid danger thus far, but since I live on an island with a thriving population of deer and rabbits, having good visibility at night is a must.
Please help!
Most likely your alternator belt is getting wet and slipping
Get one of those round wire post brushes. take the battery lugs loose, and clean the posts and the lugs. Tighen them back in place. Check the fusable link to good contact with the battery terminal. Check the ground from the battery to the frame. The symptoms you describe are often associated with a bad battery ground, and water can get into places that can cause this. It also seems to affect battery post connections, I think it is because the fumes from the battery do not have a chance to dry out in wet weather they way they do in the summer, and they cause the posts to oxidize. Another possiblity is that you have crud accumulated in the bottom of one of the battery cells, and when you hit a bump it shorts out the cell, thus reducing the total voltage. In that case you must replace the battery. good luck.
Bad belt is a good bet, tension also needs to be checked.