86 dodge ram 4x4, transfer case vaccum switch is busted and 4wd wont engage. Is there a way to bypass this switch like on a choke and use a manual cable to engage.

Hi, did you check the transfer case fluid level at all ??

Could also be your metal vaccum lines on the cross member and along the passenger side of the frame to the front axle assembly where they connect to the axle vaccum switch diaphragm. are rusty and leaking not engaging the 4 wheel drive all the way in gear.

You will probably need a shop manual to work on it yourself. The switch on the dash controls a vac servo on the transfer case. The servo controls an actuator under the battery which sends vac to the front axle. The transfer case and front axle servo work together.

Depending on the make and model, it could be the control switch on the dash or the switch that moves the gears in the transfer case.

yes check vacuum switch on top of transfer case

Ok, this is probably going to sound greek if you have no automotive experiance, so here goes:

There are 2 possibilities I can think of at the moment depending on your 4wd system, however there are several things that can cause this

If you have a Push button 4wd (you push a button or turn a knob) the system engages using actuators or sylinoids meening you turn the 4wd on, the switch sends power to the selector option (high and low) and the 4wd light on the dash. the selector determines where the actuator/silenoid engages (either high or low) in the transfer case. However the actuator or silenoid can be faulty and yet the system will say 4wd is on because the switches still sending power to the 4x4 light

The next setup is the manual linkage set up, and given the year of your kia I doubt you have this setup However I am going to go through it anyway.

With a maual linkage setup you engage the trasfer case maualy using the 4wd shifter. Ironically on newer manual shift 4wd systems the dash light is still triggered electrically by location of the shifter not what is going on in the transfer case (Ah a flaw in the design) So if you linkage is loose/bent/damaged or somehow disconnected your 4wd wont engage but the light will still show that it is! Hope this helps

check your 4x4 actuator on the passenger side of the front axle housing and make sure there is vaccum to the motor if not check the vaccum switch on the top side of the transfer case

4x4 is engaged by a solenoid on the transfer case. if water or dirt gets in it it will not work. might also a be electrical wire loose.

shift into 4wd and move truck a couple of feet.
if light is still off, park truck block the wheels set the park brake jack right front wheel and try to hand spin the wheel if wheel doesn't turn 4x4 is functioning properly but there is a wiring problem use an ohmmeter to check the 4x4 switch wiring fuse and bulb
if wheel turns freely the front axle or transfer case is not engaged
attempt to hand spin the front driveshft if the driveshaft will spin the transfer case is not engaged check the transfer case shift linkage, problem is in linkage or transfer case internals
if the driveshaft will not spin the transfer case is engaged properly
with trnsmission in neutral or park start engine measure vacuum on the two vac lines at front axle shift motor . one line should have approx 20" vacuum. other line should have none
if no vacuum measured look for vac leak or bad vac switch
if both lines have vac look for a bad vac swithc or ruptured cad actuator diaphragm
if one line has 20" +- VAC
move transfer case lever to 2wd measure vac again lines should have swapped vac signals
if no vac switch bad or 4wd shift likage needs adjusting
if yes vac motor bad or stuck or shift fork stuck
remove vac shift motor from the axle attach vac lines to shift motor engage disengage 4wd
does shift motor plunger move at least 1/2 inch
no shift motor bad
yes check axle shift fork and vac motor for binging

There are some vaccum lines that go to your axle. there is a disconnect there and a switch that lights up your dash light when engaged. I would first make sure they are still connected and not damaged. The vaccum signal to engage and disengage comes from the top of your transfer case right under the shifter boot. To test if you disconnect is working, apply vacuum to one or the other side of the diaphram for the axle disconnect and try it out. otherwise you may have lost vacuum somewhere or you have a bad switch on your transfer case.