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Topic: VDO Speedometer & Dash Lights problem. (Read 970 times) previous topic - next topic

VDO Speedometer & Dash Lights problem.

Wanted to check my mileage, turned the key on, then the dash lights to read it. When I pulled the headlight switch out, I got a strange 'buzzing' sound that changed as I rotated the rheostat (which feels rough) it alternated in sound, but never quit. The odometer was going crazy during all of this (little squiggles, flashing) It finally settled down and read correctly, but, as long as the dash lights were on, THAT SOUND was there!  Turned the key off/on again after 20 minutes, (no engine start), hit the dash lights, and the noise was less, but the odometer was still crazed until it settled down and read correctly. Any clues? Should I throw some silicone on the headlight pull/push rod, or?  :help:
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: VDO Speedometer & Dash Lights problem.

Reply #1 –
What was voltage on the dash at this time?  If steady and 12+ VDC I would check that all grounds were tight (far left side of raised part of dash.

If all that good, would probably replace the head light switch-- it could be arcing internally (there is a rheostat in it) which would drive electronics connected to it CRAZY.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: VDO Speedometer & Dash Lights problem.

Reply #2 –
Quote from: wolfe10 –
What was voltage on the dash at this time?  If steady and 12+ VDC I would check that all grounds were tight (far left side of raised part of dash.

If all that good, would probably replace the head light switch-- it could be arcing internally (there is a rheostat in it) which would drive electronics connected to it CRAZY.
Yup, 12+ VDC at the dash. I think it is arcing, (that's a good description of the sound) and it modulates as I turn the rheostat. Thanks, Brett!  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: VDO Speedometer & Dash Lights problem.

Reply #3 –
Trust me if it's only the rheostat is bad, and you dont feel the need to be able to dim the dash lights just jumper it. The Taiwan replacement switch is So bad I bought 2 both were so flimsy that the knob won't seat and hold. 20 hours of pure cussing frustration. Don't go there Mike if possible.
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: VDO Speedometer & Dash Lights problem.

Reply #4 –
Quote from: Old phart phred –
Trust me if it's only the rheostat is bad, and you dont feel the need to be able to dim the dash lights just jumper it. The Taiwan replacement switch is So bad I bought 2 both were so flimsy that the knob won't seat and hold. 20 hours of pure cussing frustration. Don't go there Mike if possible.
Explain 'jumper it', pleeze. I'm not even going to bother with fooling with it, since we hardly ever drive at nights and never use the rheostat, anyways, unless one of you 'wired wizzards' thinks it could be dangerous. Wonder if it can be cleaned?  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: VDO Speedometer & Dash Lights problem.

Reply #5 –
I removed my headlight sw. took it to car quest. They found it was a gm part, replaced it. Perfect fit lights dimmed perfectly.
1995 U320 40', 2013 chevy sonic toad, my real love are corvettes have owned 30

Re: VDO Speedometer & Dash Lights problem.

Reply #6 –
Carquest S415P bought two of them, both were flimsy and would not hold enough alignment to retain the shaft. First one lasted for about a dozen uses, and then broke it trying to bend it into alignment, second one after about 4 hrs of tweaking is holding for now. Lucky Joe. Maybe Napa has a better built switch, but we no longer have a Napa in town, and very few hard core auto parts places left.

Headlight switch removal
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: VDO Speedometer & Dash Lights problem.

Reply #7 –
My little issue is not over: just turned the ignition on to re-set the bad leveling jack (another thread  :facepalm: ) and the odometer was still going crazy, even without the dash lights on! So it goes.  :-\
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: VDO Speedometer & Dash Lights problem.

Reply #8 –
Update went to move the coach tonight, gingerly pulled the trouble prone Carquest S415P light switch it came on. After moving the coach, I attempted to shut the headlights off and switch would not budge. DO NOT BUY the very flimsy Carquest/BWD S415P switch!!! I have $36 and about 20 hours of frustration invested in these POS. Tomorrow I will try an oem acdelco D6251D switch if I can find one. Will test flimsyness before leaving store. >:D
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake
 

Re: VDO Speedometer & Dash Lights problem.

Reply #9 –
Common problem with the potentiometer.  Clean it (the old headlight switch) by rotating and spraying Deoxit D5 into it, see if it clears it up.  You can generally spray alongside the shaft, and check to see if there are any other openings in the body of the switch.  Too much won't hurt anything, just clean the other contacts inside.  This is a standard fix for older analog equipment.
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS