Detroit 60 cruise control

im trying to get the cruise control working. It’s a Detroit ddec 3 engine in a 1995 freightliner fld. The high idle works with the parking brake on.

When driving cruise does not work. I checked the clutch switch, it was broken so I looped the wires but still no cruise.

Then I noticed the brake lights are not working. Hmm maybe these problems are related.

I looked behind the brake pedal at the air manifold. It has 4 air switches. One of them is working with the brake pedal engaged, putting out a positive signal.

I could the rewire the brake lights off that. But I don’t know what to do for the cruise. Rewire to ecm? I do have the ddec pin out but I don’t know if it would get positive or ground.

Does anyone know if there’s a stop light relay? Half my relay labels are unreadable. This could be a relay problem. I’m thinking about starting by redoing the cab ground cable.

Advice appreciated.

 

ok I’ll have to check at the ecm connector that both the brake and clutch pedal switches are sending grounds. If I understand correctly.

haven’t checked that yet. On the to do list...

got some air switches. One may be for brake pedal switch which is Separate from the brake light switch. Haven’t verified that, yet.

 

Fixed the brake light problem, seems unrelated. Still no cruise.

 

Yes the park brake switch works. High idle works. But not going down road. I’m going to check this morning that the ecm is receiving ground for clutch & brake pedal switches. If ok I’ll move onto the speed sensor. The speedometer is working.

 

I looked at the speed sensor. This Eaton 10 speed has only one sensor. It’s a 4 wire speed sensor which branches off into 2 plugs.

But I didn’t need to look into that. I checked the ecm connector, which was getting a ground from the clutch switch but not from the service brake switch. These are pins j2 and g2. So I jumped the brake switch wires behind the steering column on the air switch manifold. This gave me a ground at both j2 and g2. Testing, cruise works as expected. It’s fair to say my brake switch is bad.

I think I might hook up the brake switch wire to the brake lights which run off a separate switch using a relay.

For now, problem solved. Thanks for help.