Weird electrical problem
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Joined: Jan 2013
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Weird electrical problem
Been noticing for about a week now, that when going down the highway (60-70mph), when I turn on the rt turn signal to change lanes, my auto transmission downshifts. It doesn't do this when applying the left signal. I noticed last night that my left rear brake/turn light is inop. There is no indication on the dash that a bulb is out. Front signal flashes at the normal rate. Any ideas?
Fleet Mechanic
Joined: Jan 2011
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From: 8600 ft in Colo
Are you sure the trans is actually downshifting? Could it be that the torque converter is un-locking? The PCM un-locks the TC when the brakes are applied, and senses this via the brake lights. When bulbs are out, the PCM can get confused.
Change the bulb & see what it does...
Change the bulb & see what it does...
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Ok, I'll give that a try. I had a '92 F250 that, over a several month period, lost ABS, then the speedo quit, and finally the truck wouldn't shift out of low. An honest tranny mechanic told me to fix the speedo and see what happened. I changed the ABS/speed sensor in the differential (a $20 part) and everything that had been slowly going wrong was fixed. So I've seen strange things with these trucks. I didn't equate this problem to a bulb because the dash indicator and front signal still flash at the normal frequency instead of rapidly, which is what I would expect from a bad bulb.
Thank you for the advice. I'll post the results here tomorrow.
Thank you for the advice. I'll post the results here tomorrow.
Cargo Master
Joined: Jan 2004
Posts: 3,118
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From: South Dakota
There are a couple small wires that go through the shift lever to that switch on the end of the shift lever. I imagine that plastic piece under the steering wheel that cancels the turn signal lever when the turn is completed, is hitting one of those wires and shorting it against something metal. A bare spot in one of those insulated wires. Something on that order anyway. That would be my guess.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
The fast flashing when a bulb is burned out is a function of a standard flasher. A heavy duty flasher (commonly used for towing) doesn't change the flash rate depending on lamp resistance like a standard flasher will, to accommodate the extra lamps on the trailer...
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anteru
1961 - 1966 F-100 & Larger F-Series Trucks
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Jul 21, 2010 04:53 AM
