strange speedometer

[highway star]

something weird is happening to my 260z. whenever i press the brake pedal the speedo drops to zero, then returns to the correct reading as soon as i take my foot off !. also the rev counter seems to have a mind of it's own, sometimes it'll work and sometimes it won't. i have a 280zx dizzy fitted, don't know if that's relevant. can anyone help.

 

[morbias]

It sounds like there is a short circuit somewhere (probably in the loom that connects to the back of the speedo) that grounds the speedo when the brake switch is pushed.

 

[jonbills]

speedo is mechanical isn't it? pretty sure... is it the tacho or the speedo thats going to zero?

 

[Phil240z]

Is it an electronic or mechanical speedo?

 

[moggy240]

if i remember i thought if the rev counter is disconected the car will not run and is electric

 

[highway star]

it's the speedo that's going to zero, it's a '74 260z soz not sure if it's mechanical or electric. wasn't sure which section to post the thread in.

 

[zbloke]

Is some part of the brake pedal pushing, pulling or trapping the speedo cable when its pressed?

 

[highway star]

thanks zbloke i've just checked and sure enough the pedal is pushing the cable away !. if only my brain worked in a logical way !, thanks to everyone else as well.