Rapid Turn Signal...

[castlesteve]

Anyone have this problem...

I usually diagnose problems pretty quickly, but this one is a little funny.

Model year: 1974

When the turn signal is NOT engaged, the flasher relay pulses randomly at double the normal rate.

The standard flash rate is duty cycle is determined by 2 circuits... the ON cycle is determined by the series resistance of the bulbs (about 500 ohms)... and the off cycle is determned by the RC constant in the flasher relay.

The relay is engaged when it has a low resistance to ground (less than 1k Ohms)... but should be an open circuit when not engaged.

3 items are in parallel to engage this relay (the relay is used for 3 separate functions): turnsignals, emergency flasher and emergency brake engaged.

Most people have the 3rd item disabled as they have disabled the seat belt interlock...

Replacing the relay does not fix the problem... and the emergency brake switch also seems to be ok. There is one more switch on my diagram... the emergency warning switch. Anyone know where that is????

Sorry about the lengthy technical post... just trying to reduce the amount of questions.

[John Rogers]

On our 1974 this happened and it has dirt in the emergency flasher switch. I cleaned it really good with electrical cleaner and the problem went away. The flasher circuit uses the emergency flasher switch if I remember correctly? It is just to the left of the headlight switch on our cars. Good luck.

[castlesteve]

Hmmmm... well i have an extra one i can try. For some reason i have in my head that it cant be that... ill definitely try it!

[philinjax]

Steve,
The other emergency grounding device you are looking for is the brake warning switch. This is the 4th sensor device that triggers the flasher relay. It is part of the brake master cylinder and is accuated when either the front or rear brake circuits spring a leak. However, I don't think this is the cause of the random double rate action of the flasher relay. I think it is a defective relay.
Phil

[castlesteve]

ive already replaced the relay... and it certainly is not the problem. I even bench tested the old one... and it works perfectly.

It could possibly be a bad (semi grounding due to corrosion) of the brake warning switch. I imagine that is mounted on the master cylinder???

when it stops raining ill pull the car out and look.

thanks Phil and John

[rockaria]

I have experienced this exact problem. I traced it to a turn signal light that was wired inncorrectly. (i.e. Ground on light post, light post on ground) The fuse was too big in the block and it did not pop it, all it did was to make it blink really fast when the turn signal was selected. But the relay got super hot.

As I was looking I noticed that if you get any wire crossed in the circuit that it will make the flasher go fast. At one point my dash flasher light did not work and I tried to wire it to work by crosing the actual light into the dash light and that also caused this fast flashy thing. This did not make the relay hot. I know a Du_A__ solution but it was fun.

Maybe that'll help some,