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Topic: Boost Switch Solenoid (Read 532 times) previous topic - next topic

Boost Switch Solenoid

Is there a way to check if the boost switch solenoid is working while both house and chassis batteries are fully charged? When I turn the switch on I hear the solenoid click but turning it back off there is no click. When I thought that the chassis batteries were low I left the switch on for about 14 hours but with the switch off the engine cranked like the chassis batteries were low. Since then I have been leaving an intelligent charger on the chassis batteries and the engine cranks normally. I have purchased a Trick-L-Switch which I plan to install wired to this solenoid but would still need for the solenoid to work if the alternator were to fail and I needed to get home running the house generator (been there, done that).
Thanks, Robert
Rob & Di
2001 U270 34'

Re: Boost Switch Solenoid

Reply #1 –
Quote from: Rob & Di –
Is there a way to check if the boost switch solenoid is working while both house and chassis batteries are fully charged? When I turn the switch on I hear the solenoid click but turning it back off there is no click. When I thought that the chassis batteries were low I left the switch on for about 14 hours but with the switch off the engine cranked like the chassis batteries were low. Since then I have been leaving an intelligent charger on the chassis batteries and the engine cranks normally. I have purchased a Trick-L-Switch which I plan to install wired to this solenoid but would still need for the solenoid to work if the alternator were to fail and I needed to get home running the house generator (been there, done that).
Thanks, Robert
Put a digital voltmeter on the engine battery or you could use the ignition solenoid's hot side under the dash top. When you hit the boost switch, the voltage will change at least a couple of hundreds of a volt. Leaving the boost solenoid on for any length of time generates heat in the solenoid and runs the batteries down unless connected to shore power. Even then, the boost solenoid will get hot.
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Boost Switch Solenoid

Reply #2 –
Similar test with fully charged batteries, you can just use the dash chassis battery voltmeter. Turn key to on to read dash voltmeter (don't start), turn head lights on and dash fan to high (this will draw current from chassis battery and create some voltage drop). Watch the dash voltmeter and wait a minute or so, then hit the boost switch. If boost is working you should see the dash voltmeter jump up a little. If there is no change in the dash voltmeter, boost solenoid is suspect.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Boost Switch Solenoid

Reply #3 –
You can access either the boost solenoid or the isolator, and place one DVM lead on the house battery terminal, the other on the chassis battery terminal.  Then measure the DC voltage difference.  It should be such lower (really close to zero volts) with the boost solenoid activated. Even fully charged, there should be some measurable difference.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: Boost Switch Solenoid

Reply #4 –
Thanks to all.
I tried measuring the voltage with my digital volt meter but when retrying I get varying results. As we are scheduled for some repairs this Tuesday at MOT so I think I'll let them take care of this.
Rob & Di
2001 U270 34'