Electrical Issues Rd690S 1990 speedometer and tach doesn't work

[Randolf80]

So the tach and speedometer doesn't work occasionally they come on but not consistent can't find a schematic anywhere I ohm out the speed sensor and it was in spec I'm waiting on a tach sensor to come in.. what's weird to me is there are sensors but no ECU any direction would be appreciated thanks

[T-Mack1]

Not sure, but if they both don't work at the same time,  I would think it might be a dash power supply or ground issue.  Ignition switch or fuse could also be suspect....

 

[mackey58]

Are the cables dry.or the ends bad. My 90 has no ecu its mechanical 

[mowerman]

Good luck I was also going to say ground but mechanical???????? Good question 

[Geoff Weeks]

electronic speedos came out around 1983 +/-. However my 1992 Marmon came with a cable driven speedo, but fairly sure it was one of the last.

When electronic engines and ECM's came around in the early 90's, and then the speedo's became operated on the Can Bus from the ECM.

 The early electronics had 3, 4 or 5 wires. power + and -, signal and signal ground (two grounds are combined on 3 wire speedos) and then they often have a extra wire for 2 spd axle correction. Most common are 4 wire, + and - and then two wires to the pick-up. Tach is the same but of course no 2 spd axle wire.

[Geoff Weeks]

I would think a 1990 would have a Prestolite Trekstar  electronic speedo