Turn signal problem '74 620

[PrecisionTT]

Turn signals work fine till I turn the parking lights on. When I turn the parking lights on the turn signals will flash and so will the opposite side. The side makers also flash but very faint. Has anyone come across this problem?

[datzenmike]

This is for the 620?

[PrecisionTT]

I'm sorry I forgot to say, yes it's for a 74 620

[datzenmike]

Turn signals work fine till I turn the parking lights on. When I turn the parking lights on the turn signals will flash and so will the opposite side. The side makers also flash but very faint. Has anyone come across this problem?

 

Possibly a light filament is broken and bridged across a turn signal filament? There is a harness plug behind the rear passenger side for the tail lights. Unplug and if that fixes it then the problem is at the back. If not probably a front parking/turn lamp.

 

Have you replaced or removed a bulb lately? If so you may have screwed it in wrong and the contacts on the bottom are crossed up.

[PrecisionTT]

I've traced the problem to the back. I've changed all the bulbs thinking one may be bad, but the problem continues.

[datzenmike]

Check the ground(s) back there. Black wires I think.

[PrecisionTT]

I checked the ground, and ran a separate ground wire from the tail light housing to the from. It helped a little but still flashing opposite side very faint but still flashing. Someone mentioned maybe it was back feeding to the turnsignal switch, is this possible? Thank you for your help.

[datzenmike]

Well if very faint it could be normal. My old '78 would faintly flicker the headlamps at night when signaling. The very small voltage drop from those 6? bulbs flashing was enough to dim (very slightly) the headlamps and the dash lamps too..

[PrecisionTT]

Same problem I'm having. Thank you for your help. I'll post if I find anything

[Cardinal Grammeter]

Clarification:

 

Parking Lights ON:  Turn signals work correctly on the desired side, but the other side flashes too?

 

Is the other side actually flashing the other filament OR is it really dimming the parking light bulb?  or stated differently:  does the other side flash in sync with the desired side?  or totally out of phase?

 

Because you also mention the Sides "flashing."  Could them simply be "dimming" because of the turn signal filament current draw?

 

I have my 74 620 working and the turn signals are pretty dodgy.  Its like there are issues at the blinker.  They have a "weak" flash, not light the strong "click click" of old American Iron.

 

ALSO THIS IS BIG DEAL:  My fuse box was corroded and some circuits simply did not work at all - like the Backup Lights.  Many others have run into this (not just Backup lights.)  I cleaned mine in a dentist grade ultrasonic cleaner with a dash of white vinegar.  The result was shiny copper everything and now everything worked.  It is possible you may have low voltage issues due to corrosion at the fuse block.