84 300sd cruise works perfect or not at all

[joeyg1]

Every time the car is started the cruise either comes on(25mph+) and works perfect (all functions) untill the car is shut off...or will not come on untill the key is turned off and turned back on. It only works about 25% of the time the car is started, but if it works, it it's flawlessly. If it dosn't work nothing I do will make it come on. Some time I can get it to work by turning the key off and on while driving. It's consistant, it's on or off, never messing up if it's on, or never working untill the key is turned off then back on. Anybody heard of this before?
JG

[Beastie]

oeyg1, I have the same issue on my 85. Got some great help here. Do a quick search of my threads and you will find it. I am running out the door so if you can
not find it email me and I will get it to you.
Alan

[noah brinkman]

I am going to say cruise amp
silver box above your left foot it's got like 12 pins
or atleast that is where it is on SD's and SDL's

I had similar issue I replaced the switch it worked more offten but had speed surges (toyota style)

then I swapped in a cruise amp from an 85 SD
and now I am cruisin when I want! not hit or miss

[joeyg1]

It sounds like an electronic switch(relay) that once energized won't change. It might be a solder joint but if it is, it seems too consistent with no weird behavior until the power is turned off then on. If I unplug the amp then plug it in it works everytime, but when powered off, then on, won't come on...it's a crap shoot. Works perfect, all functions until it's powered off, or nothing.

[toomany MBZ]

Just because I can't find a relay for that system, doesn't mean there isn't one.
But I can't find it.