93 IDI help!

[Black&Gold]

The transmission OD light is flashing, but i believe it is because the RPM
(Engine Speed Sensor) is messed up. the tach will not go over 1500 rpm while driving or even when pressing the gas while vehicle is in park. I cannot find a diagram showing where the ENGINE SPEED SENSOR is. also would the Throttle position sensor cause the OD light to flash? what other sensors (external from trans) would cause this? i do not have access or the money to have the codes read.
Also the Battery gauge clicks up and down, and the GP Relay clicks about 3-4 times after the Wait to Start light goes out. does this mean the relay is bad?
any help would be appreciated.

[Black&Gold]

bump for help...

[daimoku]

Autozone or Advance will read the codes for free. Could be the RPM sensor or the tachometer. The RPM sensor is located in the engine compartment next to the oil fill neck. It's a nut with two wires coming out of it. The TPS/FIPL can definitely cause the OD light to flash. The VSS, TPS/FIPL, RPM sensor and MLPS/Neutral Safety Switch among others can all cause the OD light to flash. The relay does normally click for up to 2 minutes depending on the temperature after the WTS light goes off. During the clicking, approximately 200 amps goes to the glow plugs so it's normal for the battery gauge to move up and down.

[Black&Gold]

thanks for the help. i replaced the Tach sensor and the TP sesnor, the OD light was off and all was good untill i hit the highway, the light started flashing again. i had AAMCO read the codes and it was code 62/628, TC slip on 3-2 and 3-4 shift. now about the Bat. gauge clicking, what is causing it to click? you say dependent on out side temp. but why is it clicking, is it still heating the glowplugs?

[Jhnybravo]

Actually the clicking is the glow plug relay. If you stand beside the truck with the hood up, you can really hear it. The glow plug relay cycles on/off and they draw quite a bit of current which in turn causes your battery meter to bounce. Normally the relay will cut off after it's cycled about a dozen times or so when you first crank it. Or at least that's the way it does on ours.